PUBLISHED BYIOP P UBLISHING Journalof Physicsej.iop.org/pdf/jpcm/2007_top_papers.pdf · PUBLISHED...

P U B L I S H E D B Y IOP P U B L I S H I N G

TOP PAPERS 2007 SHOWCASEOnce again we bring a selection of the top papersof the year to give an impression of the diversity,range and scientific quality of papers in Journalof Physics: Condensed Matter. The choice isdifficult because JPCM has succeeded inattracting many excellent and innovative

authors. Our very fair but rigorous referees have ensured aconsistently high standard of papers in the journal. Manymore papers were singled out with the support of referees(identifying work of the very highest importance), of readers(through high numbers of full-text downloads) and of ourBoard members (through recommending articles theyfound especially valuable) than could be featured here.

All these papers have been chosen for their excellentscience. We should never forget, though, that popular appealis also important. This year our most downloaded papershave discussed the search for a Spiderman suit and the use oflaser Raman scattering to inactivate viruses. In both cases,the impact in the popular press has greatly outweighed thatfrom the journal alone. While some may disavow it, theexcitement that can be transmitted to the population at largethrough such publicity is often important for drawing moreyoung people into science.

Picking these two papers for inclusion in this year’s toppapers was easy. It would be nice if the rest of the selectionprocess were as easy, but of course it isn’t. In the end, it ishoped that our choice of exciting papers from 2007 are alsoof great interest to you, the readers. Moreover, we hope thatthese papers give a fair flavour of the range of topics that arepublished in JPCM. Clearly they reflect the vigour that existsin the condensed matter world.

David Ferry

Editor-in-Chief

I N T H I S I S S U E

FULLCONTENTSOVERLEAF

Professor David FerryEditor-in-Chief

Optimized structure of Gd@C60.

Journal of PhysicsCondensed Matter

Alex Müller asks ‘Will we findnew high-temperature super-conductors?

Spintronics and GMR

Fighting viruses with lasers

Taming Gd ions in fullerenecages

Carbon nanomaterials in biology

Cloak of invisibility to magnets

...and much more

Condensed Matter: Top Papers 2007 Showcase 1

Condensed Matter: Top Papers 2007 Showcase

2 C o n d e n s e d M a t t e r : Top Papers 2007 Showcase

P A P E R S

Fighting viruses with lasers 4A novel technique promises to destroy micro-organisms without damaging human cells

Platinum monolayers for catalysts 4DFT calculations show that a Pt monolayer on Fe(001), a potential catalyst for fuel cells, is stable

Ferromagnetic nanorings 5Nanometre-sized ferromagnetic rings show novel physics with many potential device applications

Complex phase behaviour 5Simple model potentials can produce a wide variety of phase behaviour

Cloak of invisibility to magnets 6Proposal for a cloak to shield an object from DC magnetic fields

Flipping spin affects magnetoresistance 6Spin flipping at interfaces between two metals has a significant effect on magnetoresistance

Opening the gate to quantum computing 7Electronic structure methods can be used to model the dynamics of two-qubit gates for quantum computing

Sticky problems 7Considering how animals stick to surfaces may help to improve tire grip on wet roads

Will we find new high-temperature superconductors? 8One of its discoverers reviews how HTS occurs with a view to finding new classes of HTS materials

Ferroelectric nanostructures 8Domain size is a crucial consideration in miniaturization of ferroelectric devices

Is the stripe phase a charge density wave? 9New measurements point to the charge-density-wave nature of the stripe phase in manganites

Antiferromagnetic nanoparticles 9Antiferromagnetic nanoparticles reveal unusual magnetic properties

Spintronics and GMR 10A selection of papers discussing spin-filter tunnelling, magnetic tunnel junctions and spintronics

Wetting problem revisited 11Calculations for the wetting transition are extended by including more terms in the perturbation expansion

Molecular transport junctions 12The effects of electron–phonon interactions in molecular conduction junctions are reviewed

Clever SOD models disordered solids 12A computer program gives improved modelling of site-occupancy disorder

Half Metallic Ferromagnets 13Half metallic ferromagnets are a fundamentally different state of matter with ideally 100% spin polarization

Taming Gd ions in fullerene cages 14Encapsulating Gd within C60 enhances its correlation energies

Improvements in electrowetting 14Interfaces between two immiscible electrolytic solutions offer improved electrowetting

Carbon nanomaterials in biology 15A multidisciplinary approach is needed to study incorporation of nanomaterials in biological systems

Targeting structures by computation 15New techniques to compute a structure with a target property are more efficient

Monitoring biomolecular interactions 16Nanomaterials offer an ideal tool to monitor biomolecular interactions on a chip



Simulating charge transport in ion channels 16Charge transport in ion channels has been accurately simulated

Improved simulation of water 17Multiscale simulation of water gives an accurate description of its properties

Spinel taps rich vein of properties 17EXAFS has been used to carry out a comprehensive study of ferrite spinels

Nucleation in soft matter 18Theory of nucleation in protein solutions and colloidal suspensions is reviewed

Crystals under anisotropic stress 18A new method accounts for the effects of anisotropic stress on the structure and stability of crystals

How wetting affects drying 19Surprisingly, air flow can reduce the rate of drying of a hydrophobic porous medium

Ferromagnetic double perovskites 19Double perovskites show a range of magnetic and transport properties with potential device applications

Spin ices get stuffing 20Stuffing spin ices with extra spins appears to lead to new magnetic phases

Condensed Matter: Papers

Fighting viruses with lasers

K T Tsen (Arizona State University) and co-workers have developed a revolutionarymethod for efficient inactivation of targetmicro-organisms which avoids undesirableside effects. They accomplish this goalthrough the proper manipulation of a near-infrared femtosecond laser via impulsivestimulated Raman scattering to producedamage (e.g. on the protein coat of a virus) byforced resonance.

They measured the near-infraredfemtosecond laser-induced inactivation ofsimple viruses and bacteria, and determinedthe effects of the laser irradiation on theviability of mammalian cells. They showedthat if the wavelength and pulse width of theexcitation femtosecond laser areappropriately selected, a window in powerdensity exists that enables them to achieveselective inactivation of target viruses andbacteria without causing cytotoxicity inmammalian cells. M13 bacteriophage isdestroyed at about 60 MW/cm2 and E-coli atabout 900 MW/cm2 whereas human JurkatT-cells survive up to 20 G W/cm2. Thisstrategy targets the mechanical (vibrational)

properties of micro-organisms, and thus itsantimicrobial efficacy is likely to beunaffected by genetic mutation in the micro-organisms.

Such a method may be effective against awide variety of drug-resistant micro-organisms and has broad implications indisinfection as well as in the development ofnovel treatments for viral and bacterialpathogens. Some of the immediate plausibleapplications of this technique in biomedicalresearch will be the efficient and safetreatments of blood-borne diseases such asAIDS and hepatitis, disinfection of bloodsupply and disinfection of biomaterials inhospitals.

Inactivation of viruses with a very lowpower visible femtosecond laserK T Tsen, Shaw-Wei D Tsen, Chih-LongChang, Chien-Fu Hung, T-C Wu and JuliannG KiangJ. Phys.: Condens. Matter 19 (2007) 322102(9pp)Selective inactivation of micro-organisms with near-infraredfemtosecond laser pulsesK T Tsen, Shaw-Wei D Tsen, Otto F Sankeyand Juliann G KiangJ. Phys.: Condens. Matter 19 (2007) 472201 (7pp)

Experimental set-up for the inactivation of M13 bacteriophages. M:mirror; M.O.:focusing lens; S: sample. The magnification shows thesample area where the laser beam is focused. The cylindrical volumewhere the laser beam focuses most tightly defines the active volumefor the inactivation of M13 bacteriophages through the ISRSprocess.


A novel technique promises to destroy micro-organisms without damaging human cells

Platinum monolayers for catalysts

Polymer electrolyte fuel cells, with their highefficiency, low-temperature operation, fuelflexibility and zero-emission, offer apromising alternative to conventional powergeneration systems. One obstacle to theiruse is the high cost of platinum used tocatalyze hydrogen oxidation in the anodeand the oxidation reduction reaction in thecathode. An overlayer structure of Pt on anon-noble metal has been proposed as apotential alternative to pure Ptelectrocatalyst.

The structure’s stability is crucial forpotential catalyst applications. H Kasai andcolleagues at Osaka University investigatedthe atomic structure and stability of a Ptmonolayer on Fe(001) using spin-polarizedDFT-based total energy calculations. Theirresults showed that addition of a Ptmonolayer on Fe substrate completelyremoves Fe(001) surface relaxation andinduces minimal disordering of Fe atoms inthe interior region in accordance withexperimental findings. Pt binding on Fe is

observed to be stronger than on itscorresponding pure metal slab. Suchstabilization of a Pt monolayer on Fe(001) isverified by an accumulation of chargedensity within the Pt–Fe interface. Anincrease in charge density is also observed

within the second Fe–Fe interlayer,consistent with the contraction of such aninterlayer upon Pt layer binding on Fe.

Stability also requires the understandingof other non-trivial issues such as thestability of the structure against adsorbates,water or an acid environment which may beconsidered for a more realistic simulation offuel cell operating conditions. This study,however, presents the stability of the systemwith respect to reconstructions and surfacerelaxations which clarifies the system’sstructure, thus providing fundamentalinsights on which further rational cathodecatalyst design may be based.

First-principles investigation on theatomic structure and stability of a Ptmonolayer on Fe(001)M C Escaño, H Nakanishi and H KasaiJ. Phys.: Condens. Matter 19 (2007) 482002(7pp)

Charge density difference (positive) distribution at an isosurface valueof 0.200 eV Å -3 for Pt monolayer on /Fe(001), showing increasedcharge distribution within the Pt–Fe interface, more specifically nearPt atom sites, and bonds indicating strong Pt–Fe binding. Depletionof charge density is observed in Fe–Fe interfaces.

DFT calculations show that a Pt monolayer on Fe(001), a potential catalyst for fuel cells, is stable

http://www.iop.org/EJ/abstract/-search=46358496.2/0953-8984/19/32/322102


http://www.iop.org/EJ/abstract/0953-8984/19/48/482002



Ferromagnetic nanorings

Ferromagnetic metal rings of nanometrerange widths and thicknesses exhibitfundamentally new spin states, switchingbehaviour and spin dynamics, which can beprecisely controlled via geometry, materialcomposition and applied field. Following thediscovery of the ‘onion state’, whichmediates the switching to and betweenvortex states, many fascinating phenomenahave been found in these structures.

In this article J A C Bland (Cambridge) andmany co-workers from Europe and MIT,review their work on magnetic ringelements. The geometric parameters of ringelements determine the exact equilibriumspin configuration of the domain walls ofrings in the onion state; such behaviour canbe understood as the result of competitionbetween the exchange and magnetostaticenergy terms.

Electron transport provides an extremelysensitive probe of the presence, spatiallocation and motion of domain walls, which

determine the magnetic state in individualrings, while magneto-optical measurementswith high spatial resolution can be used toprobe the switching behaviour of ringstructures with very high sensitivity. Thering geometry has been used to study manymagnetic phenomena, including the

displacement of domain walls by electriccurrents, magnetoresistance, the strength ofthe pinning potential introduced bynanometre size constrictions, the effect ofthermal excitations on the equilibrium stateand the stochastic nature of switchingevents.

This precise control of the magnetic ringcharacteristics makes it a very attractivegeometry for devices, including MRAM andmagnetic sensors.

Ferromagnetic nanoringsC A F Vaz et alJ. Phys.: Condens. Matter 19 (2007) 255207(14pp)

This is part of a special issue containing papersfrom the European Science Foundation Workshopon Mott's Physics in Nanowires and QuantumDots (31 July–2 August 2006, Cambridge, UK)J. Phys.: Condens. Matter 19 Number 25.

M–H loop of an array of polycrystalline Co rings, 1.65 Ìm outerdiameter, 350 nm wide, 16 �m thick. The insets show schematicdiagrams of the onion and vortex states which are attained during themagnetization reversal process.

Nanometre-sized ferromagnetic rings show novel physics with many potential device applications

Complex phase behaviour

G Malescio (Messina) reviews the use ofeffective potentials as a simple way torepresent complicated interactions. It isespecially relevant to soft matter systemswhich generally consist of mesoscopicparticles with supramolecular architecturelargely susceptible to external agents, such ascolloidal systems, polymers, and surfactants.Soft matter offers the possibility to tuneinteractions at a microscopic level. This hasincreased the scope of observable phasephenomena and widened the range ofinteraction model potentials of physicalrelevance. Such potentials, when applied tomolecular systems, contain, in a condensedform, information about the internal degreesof freedom of the macromolecule, so theymay give rise to phase behaviour radicallydifferent from that of typical monoatomicsubstances.

The concept of intermolecular effectivepotential has proved useful for a broad rangeof problems, but as it is based onapproximations that are not always satisfied,it is inadequate for a number of systemswhen ab initio simulations are appropriate.Although time consuming, thesecalculations are intrinsically more accuratethan those based on effective interactions.As computing power increases, theusefulness of intermolecular potentials

comes into question. Undoubtedly, theability to simulate a phenomenon accuratelyis invaluable, and may even provide acheaper alternative to experiment, butreproducing reality is not necessarilytantamount to understanding it. The abilityto describe a phenomenon using simpleideas and concepts is the basis for enhancedcomprehension.

Malescio reviews a number of simplemodel potentials presenting unusual

features and discusses the role of attractionand repulsion in determining their phasebehaviour.

Complex phase behaviour from simplepotentialsG MalescioJ. Phys.: Condens. Matter 19 (2007) 073101(23pp)

Simple model potentials can produce a wide variety of phase behaviour

Spatial configuration for a 2D system interacting through the simple potential u (r) = � (r < �); -= �(� < r < � + �), = 0 (r > � + �), where � isthe particle diameter and � is the height of the repulsive shoulder with � = 1.5 �, immediately above and below the transition to the stripephase.





Flipping spin affects magnetoresistance

While initial analyses of giantmagnetoresistance in ferromagnetic/non-magnetic metallic multilayers assumed thatthe direction of the spin of each electronstayed fixed as it transited the multilayer, wenow know that this is only true in a certainlimit. Generally, the spins ‘flip’ in a distancecharacteristic of the metal, its purity, and thetemperature.

A review by Jack Bass and William Pratt ofMichigan State University describes how tomeasure the lengths over which electronmoments flip in pure metals and alloys, andthe probability of spin-flipping at metallicinterfaces. Spin-flipping within metals isdescribed by a spin-diffusion length which,in certain simple cases, sets the distance overwhich the magnetoresistance decreases(increases) as the nonmagnetic(ferromagnetic) layer thickness increases.Spin- flipping at interfaces between metalsM1 and M2 can be described by a parameter,�M1/M2, which determines the spin-flipping

probability, P = 1 – exp(–�). Increasing �M1/M2

usually decreases the magnetoresistance.The authors list measured values of theseparameters and discuss the limitations on

their determinations.Because of both experimental and

theoretical uncertainties, it is important tocompare values for nominally identicalparameters determined in different ways.Making such comparisons possible is one ofthe tasks of this review. The authorssometimes have clear views as to which ofthe conflicting analyses and derived valuesare most reliable. They explain theirreasoning, but warn that others will notnecessarily agree.

Spin-diffusion lengths in metals andalloys, and spin-flipping at metal/metalinterfaces: an experimentalist’s criticalreviewJack Bass and William P Pratt JrJ. Phys.: Condens. Matter 19 (2007) 183201(41pp)

Lateral (L) geometries for standard and non-local (NL)measurements. (a) lateral spin-valve film with standard (#1) andnon-local (NL) (#2) current and voltage connections. (b) LNL cross(LNL/C) geometry with F1 and F2 layers of different widths. (c)LNL/+ geometry with additional N2 and/or F3 cross-strips. (d)LNL/TT three-terminal device.

Spin flipping at interfaces between two metals has a significant effect on magnetoresistance

Cloak of invisibility to magnets

In so-called metamaterials themicrostructure is engineered to achieveproperties not found in nature. It is knownthat they can cloak objects from microwavesbut B Wood and J B Pendry (Imperial College,London) have designed metamaterials thatfunction at very low frequencies, usingsuperconducting components to controlanisotropic diamagnetism.

They showed that solid cubes ofsuperconducting material (which is close to aperfect diamagnetic material) arranged on asimple cubic lattice with cube sizeapproaching the lattice constant can achievean effective permeability between 0 and 1but it is not anisotropic. They make thesystem anisotropic by flattening the cubesinto very thin plates. There will be noappreciable electric response perpendicularto the plates, but parallel to them the electricresponse is similar to the cubes. Conversely,there is little response to a magnetic fieldparallel to the plates, and a weakeneddiamagnetic effect normal to them. Similarresults are obtained if the cubes are replacedby spheres and the plates by discs.

To build a magnetic cloak, we need ananisotropic material which is diamagnetic orparamagnetic depending on the fielddirection. These superconducting

metamaterials are diamagneticperpendicular to the plates and the effectivepermeability in this direction can be tunedby adjusting the plate size and spacing. Acomponent which will provide ananisotropic paramagnetic response alsoneeds to be incorporated. This is achieved byalternating layers of superconducting plateswith a material with high permittivity, highresistivity and low hysteresis, such as certainferrites or amorphous metals.

The figure illustrates a section through thecloaking structure. Decreasing the size ofthe plates or making the gaps larger as wemove outwards, can achieve the desired

variation in radial permittivity.

Metamaterials at zero frequencyB Wood and J B PendryJ. Phys.: Condens. Matter 19 (2007) 076208(9pp)

An alternative route to negative refraction isgiven by Jingsong Wei and Mufei Xiao, whoconsider mixing ferromagnetic materialswith nonmagnetic microscopic particles.The ferromagnetic material provides theneeded permeability via domain wallresonances at high frequencies, whereas thenonmagnetic material gives the requiredpermittivity. Using effective medium theory,they found that when the concentration ofthe nonmagnetic particles falls into a certainrange, the refractive index of the mixture isnegative. They give the requirements on themicroscopic material properties for theferromagnetic materials to reach the domainwall resonances at high frequencies.

Negative refraction via domain wallresonances in a homogeneous mixture offerro- and nonmagnetic substancesJingsong Wei and Mufei XiaoJ. Phys.: Condens. Matter 19 (2007) 072203(7pp)

The proposed magnetic cloak; the shaded region in the centre ishidden from external magnetic fields. The plates form broken circles(in cross section); the full circles show the ferrite or amorphous metal.

Proposal for a cloak to shield an object from DC magnetic fields






Sticky problems

Surface roughness is the main reason whymacroscopic solids do not usually adhere toeach other. Biological adhesion systems usedby insects and some geckos are built fromrelatively stiff material, but strong adhesionis possible even to very rough substratesurfaces by using non-compact solidstructures consisting of either fiber-platearray structures or foam-like structures.

To optimize the binding to rough surfaceswhile avoiding elastic instabilities, e.g. lateralbundling of fibers, spiders and geckos use ahierarchical building principle, where thethickness of the fibers and plates (or walls)decreases towards the outer surface of theattachment pad. The thickness of the fibersand plates at the surface of the attachmentpads is so small that strong (dry) adhesion ispossible even to very rough substrates.

However, for most insects and for treefrogs, the thickness of the fibers and plates(or walls) is so large that negligible adhesionwould probably occur to most naturalsurfaces if both the pad surface and thesubstrate surface were dry. For this reasonflies, bugs, grasshoppers and tree frogs injecta wetting liquid into the pad–substratecontact area, which generates a relativelylong-range attractive interaction due to theformation of capillary bridges. The liquidinjected by insects seems to be a two-component emulsion comprising a lipid-likefraction and water-soluble nano-droplets.

B N J Persson ( Jülich) discusses someaspects of wet adhesion for tree frogs. Some

of the results may also be relevant for sometechnological applications, e.g. tires on wetroad surfaces.

Wet adhesion with application to treefrog adhesive toe pads and tiresB N J PerssonJ. Phys.: Condens. Matter 19 (2007) 376110(16pp)

Spiderman suitNicola M Pugno (Politecnico di Torino)discusses adhesion of spiders in terms ofnanointerlocking, capillary and van derWaals forces, showing the key role played byhierarchy in the design of superhydrophobicand superadhesive materials. He quantifiesthe reversibility of the strong attachmentusing a nonlinear peeling model includingfriction. He suggests that we can mimicnature, using carbon-nanotube-based

technology, to make large invisible cables, aswell as self-cleaning, superadhesive andreleasable hierarchical smart materials. Hefound that a man could theoretically besupported by a transparent cable with cross-section of 1 cm2 and feasibly, with spidermaterial gloves and boots, remain attachedeven to a ceiling: a preliminary step towards aSpiderman suit.

Towards a Spiderman suit: large invisiblecables and self-cleaning releasablesuperadhesive materialsNicola M PugnoJ. Phys.: Condens. Matter 19 (2007) 395001(17pp)

Considering how animals stick to surfaces may help to improve tire grip on wet roads

Opening the gate to quantum computing

Just as classical computers use networks ofstandard gates to manipulate bits, quantumcomputers use networks of quantum gates tomanipulate qubits. But quantum computinguses entanglement as a resource, the specialquantum dance that correlates thebehaviours of these qubits.

A Kerridge, A H Harker and A MStoneham (University College, London) havelooked at the dynamics of quantum gateoperation. They consider an important classof solid-state gates — those employingoptically-controlled electron spin qubits.Such gates form the basis of a possiblerealisation of the basic component of aproposed quantum information processorthat might even operate at usefultemperatures.

Their approach took a time-dependentconfiguration interaction method to studyhow the electronic structure of two electronspin qubits evolved when they interactedwith a third, optically-excited, control spin inan applied magnetic field. They couldidentify unitary operations whichapproximately disentangle the control spin,and use these operations to construct high-accuracy two-electron operations that werelocally equivalent to the standard CNOT,SWAP, and root-SWAP operations. Theycould then estimate the accuracy of a set ofcandidate quantum gates, evaluating theresidual entanglement of the controlelectron and overall gate operation times.Their results attest to the feasibility of thesilicon-based quantum gates proposed by

Stoneham, Fisher and Greenland in 2003. Whilst it is important to show that high

accuracy gates are possible, what isparticularly novel is their demonstration thatstate-of-the-art electronic structuremethods can be used to model the dynamicsof two-qubit gates, a significant advanceover previous analytical studies. Theirapproach can be generalised to multiqubitsystems, and is the basis of a powerful tool tooptimise a number of solid-state routes toquantum information processing.

Electron dynamics in quantum gateoperationA Kerridge, A H Harker and A M StonehamJ. Phys.: Condens. Matter 19 (2007) 282201(7pp)

Electronic structure methods can be used to model the dynamics of two-qubit gates for quantum computing

During pull-off an opening crack propagate (velocity v) at the pad substrate interface.






Will we find new high-temperaturesuperconductors?

Over two decades have passed since thediscovery by Bednorz and Müller ofsuperconductivity in LaCuO4, in which CuO2

planes exist, when it is doped with holes.Other cuprates have been found whichcontain the same CuO2 planes and showsubstantially higher transition temperatures.However, in the 20 years since the discoveryof HTS no other class of materials has beenfound which exhibits this property aboveliquid nitrogen temperatures. With a view tofinding another class, Alex Müller reviewswhy these exceptional properties occur, oneof the most important unsolved problems inpresent day physics.

He sketches experimental and theoreticalresults which may lead to an understanding.After describing confirmed properties andtheories, Müller discusses isotope effects,bipolarons and fermions, the intersiteJahn–Teller bipolaron as the generic

quasiparticle, the symmetry of thesuperconducting wavefunction and the roleof antiferromagnetism.

On the superconductivity in hole dopedcupratesK A MüllerJ. Phys.: Condens. Matter 19 (2007) 251002(13pp)

One of its discoverers reviews how HTS occurs with a view to finding new classes of HTS materials

Ferroelectric nanostructures

The size of ferroelectric devices continues todecrease since reducing the film thicknessincreases the capacitance for capacitor anddynamic random access memoryapplications (DRAM), and decreases thecoercive voltages for non-volatileferroelectric random access memories(NVFRAM). However, it seems that theultimate limits of ferroelectric film thicknessreduction have already been reached forplanar devices. The reduction of lateral sizein ferroelectric memories is alsoapproaching its practical limits. The nextstep in device miniaturization is thus not inthe reduction of film thickness or lateral size,but in the achievement of ever-smaller 3Dstructures such as trenches or nanotubes.

G Catalan and J F Scott (Cambridge) and ASchilling and J M Gregg (Belfast) have studiedthe scaling of periodic domain structures inferroelectric single-crystal pillars as afunction of their lateral dimensions. Theexperimental results for BaTiO3 wererationalized in terms of minimization of thetotal free energy of the crystal, including thecontributions from domains and domainwalls.

They extend the range of applicability ofKittel’s law (ferromagnetic domain sizescales as square root of crystal thickness) toferroic domains in 3D shapes. They find thatthe two in-plane directions are notequivalent in the modelling, with dominancedetermined by depolarization effects. Thedomain size is smaller in three-dimensionalstructures than in thin films of comparablethickness, which suggests an enhanced rolefor domains and domain walls in the new 3Darchitectures.

Domains in three-dimensionalferroelectric nanostructures: theory andexperimentG Catalan, A Schilling, J F Scott and J MGreggJ. Phys.: Condens. Matter 19 (2007) 132201(7pp)

In another paper the same authors derive ageneralized ferroic scaling factor and use it tocalculate the domain wall thickness andgradient coefficients (exchange constants) insome materials.

Their analysis supports the view that thethickness of 180� domain walls inferroelectrics is extremely narrow (of theorder of one unit cell), and that regularpatterns of sub-micron size domains can beachieved in photonic crystals.

Wall thickness dependence of the scalinglaw for ferroic stripe domainsG Catalan, A Schilling, J F Scott and J MGreggJ. Phys.: Condens. Matter 19 (2007) 022201(7pp)

Domain configuration in the tetragonal pillars, and schematic of thedomain symmetry.

Stripe formation at T* for La2-x SrxCuO4, x = 0.15. Pictorial views ofthe distorted CuO6 octahedra (left side) of the ‘LTT type’ assigned tothe distorted (D stripes) of width 8 Å and of the undistortedoctahedra (U stripes) of width L 16 Å. The superlattice of quantumstripes of wavelength d = L + W is shown in the upper part

Domain size is a crucial consideration in miniaturization of ferroelectric devices






Is the stripe phase a charge density wave?

Groups from Los Alamos, Cambridge andEdinburgh have collaborated to analyse heatcapacity measurements on three manganitecompounds, La0.5Ca0.5MnO3,La0.48Ca0.52MnO3 and Pr0.48Ca0.52MnO3. Theyestablished that the transition at which thestripe phase appears in manganites is secondorder, and is accurately modelled as a Peierlstransition in a material which is disorderedor contains impurities. This is the expectedbehaviour of a charge density wave in adisordered system, in contrast to thepreviously accepted picture of chargeslocalised at atomic sites.

Previous studies had concluded that theonset of the stripe phase was associated withthe simultaneous onset of ferromagnetismin La0.5Ca0.5MnO3. They found that thetransitions in materials with and without aferromagnetic signal share a commonorigin, since the entropy change at thetransition is very similar for all threecompounds. However, the origin is notassociated primarily with magnetic orderbecause, while the magnetisation varies by afactor of 100 between the compounds, thechange in entropy remains roughly constant.

This overturns the traditional view, andsuggests instead that the transition inLa0.5Ca0.5MnO3 is driven mainly by a Fermi-surface instability. This result adds to thegrowing body of evidence that the stripe andferromagnetic phases are much more similarthan previously thought, and indicates thatthe colossal magnetoresistance present inmanganites is driven by the delicate balance

between the ferromagnetic and stripe phase.These results call for a re-evaluation of the

many strongly correlated electron systemswhich exhibit stripe and checkerboardphases (e.g. cuprates, nickelates andcobaltites) in terms of a disordered chargedensity wave model which producesinsulating behaviour without the need toinvoke strong electron-phonon coupling.

Evidence for the charge-density-wavenature of the stripe phase in manganitesS Cox, J C Lashley, E Rosten, J Singleton, A JWilliams and P B LittlewoodJ. Phys.: Condens. Matter 19 (2007) 192201(7pp)

Fitting of transition peaks for three compounds to a model of a Peierlstransition in a system with impurities (a linear background wasremoved). Points are data and the solid line is the fit of the model tothe data.

New measurements point to the charge-density-wave nature of the stripe phase in manganites

Antiferromagnetic nanoparticles

Nanoparticles of magnetic materials havedifferent properties from the bulk and havenumerous technological applications.Ferromagnetic or ferrimagnetic particles aremostly used, but nanostructuredantiferromagnetic materials also haveimportant applications in, for example, spinvalves and magnetic random access memoryand in new types of hard magnetic materialsconsisting of composites ofantiferromagnetic and ferro- orferrimagnetic nanoparticles.

Steen Mørup and colleagues from theTechnical University of Denmark review themagnetic properties of antiferromagneticnanoparticles. Their magnetic moment ismainly due to imperfections or finite-sizeeffects, leading to an increase of saturationmagnetization with decreasing particle size,but thermoinduced magnetization alsocontributes to the moment of very smallparticles.

The magnetic excitations ofantiferromagnetic nanoparticles at lowtemperatures are dominated by the uniformexcitations (q = 0 spin waves). This leads to alinear decrease of the sublatticemagnetization and an increasing small net

magnetic moment as the temperatureincreases. They have a much larger excitationenergy of the uniform mode than that offerro- and ferrimagnetic nanoparticles, buteven a small uncompensated moment canhave a significant influence on the excitationenergy. Interactions between nanoparticlescan have a large influence on the magneticdynamics, e.g., the superparamagneticrelaxation. The dipole interaction betweenantiferromagnetic nanoparticles is usually

negligible, so they present a uniquepossibility to study exchange interactionsbetween magnetic particles. The interactionscan have a significant influence on both themagnetic dynamics and the magneticstructure. Nanoparticles can be attachedwith a common crystallographic orientationsuch that both the crystallographic and themagnetic order continue across theinterfaces.

Experimental and theoretical studies ofnanoparticles of antiferromagneticmaterialsSteen Mørup, Daniel E Madsen, CathrineFrandsen, Christian R H Bahl and Mikkel FHansenJ. Phys.: Condens. Matter 19 (2007) 213202(31pp)

Schematic illustration of a network of interacting �-Fe2O3

nanoparticles.

Antiferromagnetic nanoparticles reveal unusual magnetic properties





Spintronics and GMRThe 2007 Nobel Physics Prize was awarded forthe discovery of Giant Magnetoresistance(GMR), one of the key concepts in spintronics.Several of our top papers were in this area,including a special issue on Spin Electronics: J. Phys.: Condens. Matter 19 (2007) Number 16.Some of the most interesting papers in thisissue are summarized here.

Spin-filter tunnellingSpin-filter tunnelling using ferrite barrierscould generate spin-polarized electrons atroom temperatureSpin filter tunnelling is reviewed by JagadeeshMoodera and colleagues at MIT. Thisphenomenon enables highly spin-polarizedcharge carriers to be generated fromnonmagnetic electrodes using magnetictunnel barriers. The effect has been shown inmagnetic semiconducting europiumchalcogenides. If challenging material-relatedissues can be addressed, using ferrites andother methods would enable room-temperature operation, leading to hugeprogress in spin injection and detection insemiconductors.

In contrast to conventional SPT devices

using a ferromagnetic metal as the source forspin-polarized electrons, the novel approachof spin-filter tunnelling uses a ferromagnetictunnel barrier to generate a polarized current.This spin-filter effect is shown schematically inthe figure. In such a ferromagneticsemiconducting barrier, in the magneticallyordered state, exchange splitting of theconduction band creates two different tunnelbarrier heights for spin-up and spin-downelectrons.

Generating a nearly fully polarized beam ofelectrons is an extremely useful tool forfundamental studies as well as for applicationin spintronics, especially for spininjection/detection in semiconductors.

Because Eu chalcogenides areferromagnetic only at low temperature, it isattractive to use ferrites, which have TC above

room temperature. However, understandingand controlling the structure, stoichiometryand magnetic properties of ultrathin layers ofcomplex oxides is challenging. The interfacialcompatibility and bond-driven, intrinsicmagnetic behaviour can be different fromwhat one expects for the ferrites. All theseproblems have to be solved before theirpotential can be realized.

The phenomena of spin-filter tunnellingJagadeesh S Moodera, Tiffany S Santos andTaro NagahamaJ. Phys.: Condens. Matter 19 (2007) 165202(24pp)

Magnetic tunnel junctionsMagnetic nanoparticles can be used incancer therapy either for drug delivery orfor destroying the tumour by heatingC Tiusan et al (Nancy University) comparedtheoretical predictions of spin transport andwavefunction filtering in terms of symmetryin single-crystal magnetic tunnel junctionswith experimental work on Fe/MgO/Fe typeMTJs. In the equilibrium regime, when thejunctions are not biased, spin polarized tunneltransport leads to antiferromagnetic exchangeinteractions.

They also presented an interesting class ofdouble barrier system combining a classicFe/MgO MTJ and an artificialantiferromagnetic subsystem in which themagnetic properties are controlled bycoupling by spin polarized tunnelling.

Spin tunnelling phenomena in single-crystal magnetic tunnel junction systemsC Tiusan, F Greullet, M Hehn, F Montaigne, SAndrieu and A SchuhlJ. Phys.: Condens. Matter 19 (2007) 165201(35pp)

Zhanjie Li and colleagues at Grandis Inc.present experimental and numerical results ofcurrent-driven magnetization switching inmagnetic tunnel junctions. The experimentsshow that, for MgO-based MTJs, thetunnelling magnetoresistance ratio is as largeas 155% and the intrinsic switching currentdensity is as low as 1.1 106 A cm-2. Theyidentified three distinct switching modes,thermal activation, dynamic reversal, andprecessional process. They discussed therequirements for the successful application ofspin-transfer torque as the write scheme inrandom access memory.

Spin-transfer torque switching inmagnetic tunnel junctions and spin-transfer torque random access memoryZhitao Diao, Zhanjie Li, Shengyuang Wang,Yunfei Ding, Alex Panchula, Eugene Chen,Lien-Chang Wang and Yiming Huai

J. Phys.: Condens. Matter 19 (2007) 165209(13pp)

SpintronicsTomasz Dietl (Polish Academy of Sciences)reviews the origin of ferromagnetic responsein diluted magnetic semiconductors andoxides. He considers four classes:

Composite materials in whichprecipitations of a known magneticcompound account for magneticcharacteristics.

Alloys showing chemical nanoscale phaseseparation into regions with small and largeconcentrations of the magnetic constituent.He describes novel methods to control thisspinodal decomposition.

Semiconductors such as (Ga, Mn)As,heavily doped p-(Zn, Mn)Te, which provide abasis for magnetization manipulation andswitching.

Some carrier-doped DMSs and DMOswhere competition between long-rangeferromagnetic and short-rangeantiferromagnetic interactions and/or theproximity of the localization boundary lead toan electronic nanoscale phase separation.These materials exhibit characteristics similarto colossal magnetoresistance oxides.

Origin of ferromagnetic response indiluted magnetic semiconductors andoxidesTomasz DietlJ. Phys.: Condens. Matter 19 (2007) 165204(15pp)

As spintronics goes nano, new phenomenaare predicted resulting from the interplaybetween spin-dependent transport and single-electron physics. Manipulating spins one-by-one could open the path to quantumcomputing, so there is a growing effort toconnect spin tanks (i.e. ferromagnetic leads) tosmaller and smaller objects. As the dimensionsare reduced, spin-dependent transport ispredicted to interplay with quantum and/orsingle-electron charging effects.

Pierre Seneor et al (CNRS/Thales) reviewexperiments and theories on the interplaybetween Coulomb blockade and spinproperties (namely magneto-Coulombeffects) in structures where a single nano-object is connected to ferromagnetic leads.They discuss future directions in the emergingfield of nanospintronics towards quantumdots, carbon nanotubes and single moleculemagnets.

Nanospintronics: when spintronics meetssingle electron physicsPierre Seneor, Anne Bernand-Mantel andFrédéric PetroffJ. Phys.: Condens. Matter 19 (2007) 165222(22pp)

A selection of papers discussing spin-filter tunnelling, magnetic tunnel junctions and spintronics

Schematic diagram of the tunnelling spin-filter effect in a metal/EuOspin filter/metal tunnel junction. Electrons with randomly orientedspins tunnel from the Fermi level of the nonmagnetic metal throughthe EuO spin-filter barrier. The spin-split conduction band offerromagnetic EuO creates a lower barrier height for spin-up electrons( ) and higher barrier height for spin-down electrons ( ),giving rise to a highly spin-polarized current.

☞☞









Wetting problem revisited

The nature of the wetting transition of theIsing model is a long-standing unsolvedproblem. The top papers of 2006 included anew coarse-grained description of wetting inthe 3D Ising model by Andrew Parry andcolleagues at Imperial College London whichaccounts for missing physics in the originalinterfacial description. In that paper, theyshowed how a non-local effectiveHamiltonian for short-ranged wetting maybe derived from an underlyingLandau–Ginzburg–Wilson model.

Now they have combined the Green’sfunction method with standardperturbation theory to determine thegeneral diagrammatic form of the bindingpotential functional beyond the double-parabola (DP) approximation for theLandau–Ginzburg–Wilson bulk potential.They have shown that the diagrammaticmethod introduced in their first papercombines rather nicely with perturbationtheory and allows them to derive the generalstructure of the binding potential functionalW. While this contains some new diagrams

describing curvature corrections and tubeinteractions, these are of negligibleimportance for wetting. The dominantdiagrammatic structure of W is the same asthat derived for the DP model, albeit withslightly shifted coefficients. They havedetermined the values of these coefficientsexactly. They also showed how all thediagrams in the asymptotic expansion of W(up to two tubes) simplify for wetting at

planar substrates. While some localcontributions are accurately described by abinding potential function and position-dependent stiffness, the non-localcontributions generate weak long-rangedtwo-body interfacial interactions, whichplay a crucial role at critical wetting.

Derivation of a non-local interfacialHamiltonian for short-ranged wetting:II. General diagrammatic structureA O Parry, C Rascón, N R Bernardino and J M Romero-EnriqueJ. Phys.: Condens. Matter 19 (2007) 416105(21pp)

Schematic diagram showing a wetting layer of phase ‚ at a non-planar wall–· interface. Here, l(x) and „(x) are the interfacialcollective coordinate and wall height, respectively.

Calculations for the wetting transition are extended by including more terms in the perturbation expansion

1. High ImpactJPCM’s Impact Factor is on anupward trend. It is currently 2.038and as the journal continues toattract the very best submissionsis expected to rise further.

2. Fair refereeingWith a 2007 rejection rate of 54%,JPCM’s fair but rigorous refereeingensures the journal publishesresearch of the highest quality.

3. Global visibilityJPCM is available in over 1800 institutions and is read byresearchers at the top researchorganisations across the world.

4. Rapid publication processIn 2007 the median number of days from receipt to first decision was only 39 days.

FOUR REASONSWHY TOPAUTHORS PUBLISH IN JPCM

Do you want to know more? For more information about submitting to the journal, including full author guidelines, visit www.iop.org/journals/authorsubs

www.iop.org/journals/jpcm

0

0.5

1.0

1.5

2.0

2.5

2002 2003 2004 2005year

impa

ct fa

ctor

20060

500

1000

1500

2000

num

ber o

f arti

cles

2500

2004 2005 2006 2007year

submittedaccepted

UK

Europe

North andSouth America

ROW

Asia

0

10

20

30

40

2003 2004 2005 2006year

med

ian

time

to fi

rst d

ecisi

on

2007




Molecular transport junctions

In molecular transport junctions, thesimplest components of molecularelectronics, a molecule is inserted betweentwo electrodes, and subjected to an appliedvoltage. Michael Galperin and Mark ARatner of Northwestern University andAbraham Nitzan of Tel Aviv Universitypresent an overview of the effect ofelectron–phonon interactions in molecularconduction junctions. The interplaybetween electronic and nuclear dynamics inmolecular systems is a significant factor inmolecular energetics and dynamics withimportant implications for molecularstructure, spectroscopy, electron transferand chemical reactions.

Recently, the study of transport ofelectrons in single molecule junctions hasbeen extended to probe beyond the simpletunnelling associated with large energy gapsbetween electrode Fermi level and molecularlevels, to deal with smaller gaps, with near-resonance tunnelling and, particularly, witheffects due to interaction of electronic andvibrational degrees of freedom.

After a short experimental overview, anddiscussion of different test beds andmeasurements, the authors use a simplemicroscopic model Hamiltonian to discussphenomena including: transition fromcoherent to incoherent transport aselectron/vibration interaction increases in

strength, inelastic electron tunnelingspectroscopy and its interpretation andmeasurement, affects of interelectronicrepulsion treated at the Hubbard level, noisein molecular transport junctions, non-linearconductance phenomena, heating and heatconduction in molecular transport junctionsand current-induced chemical reactions.

The review finally points out directions inwhich further research is required to answercardinal questions concerning the behaviourand understanding of vibrational effects inmolecular transport junctions.

Molecular transport junctions:vibrational effectsMichael Galperin, Mark A Ratner andAbraham NitzanJ. Phys.: Condens. Matter 19 (2007) 103201(81pp)

A contour map of the differential conductance (left), and the conductance derivative (right). Non-resonance (IETS) features are seen in theconductance derivative map in the non-conducting regions of this diamond diagram.

The effects of electron–phonon interactions in molecular conduction junctions are reviewed

Clever SOD models disordered solids

Examples of site-occupancy disorder, thenon-periodic occupation of lattice sites in acrystal structure, are metallic alloys, mineralsolid solutions, and synthetic non-stoichiometric compounds. Theexperimental investigation of thesematerials only provides averagedinformation of their properties. Computer-modelling techniques make valuablecontributions to the investigation of site-occupancy disorder in solids, by evaluatingthe relative stabilities of configurations usingsimple energetic criteria.

R Grau-Crespo and colleagues atUniversity College London present amethodology, which reduces the number ofsite-occupancy configurations to becalculated when modelling site disorder insolids, by taking advantage of the crystalsymmetry of the lattice. Within thisapproach, two configurations are consideredequivalent when they are related by anisometric operation; a trial list of possible

isometric transformations is provided by thegroup of symmetry operators in the parentstructure, which is used to generate allconfigurations via atomic substitutions.

They have adapted the equations forconfigurational statistics to operate in thereduced configurational space of theindependent configurations. Each

configuration in this space is characterizedby its reduced energy, which includes notonly its energy but also a contribution fromits degeneracy in the completeconfigurational space, via an entropic term.They present the new computer programSOD (site-occupancy disorder), whichperforms this analysis in systems witharbitrary symmetry and any size of supercell.As a case study they use the distribution ofcations in iron antimony oxide FeSbO4,where they also introduce some generalconsiderations for the modelling of site-occupancy disorder in paramagneticsystems.

Symmetry-adapted configurationalmodelling of fractional site occupancy insolidsR Grau-Crespo, S Hamad, C R A Catlow andN H de LeeuwJ. Phys.: Condens. Matter 19 (2007) 256201(16pp)

Two configurations are considered equivalent if there is an isometrictransformation, a geometric operation (e.g. translation, rotation,reflection) that keeps constant all the distances and angles, thatconverts one into the other.

A computer program gives improved modelling of site-occupancy disorder





Half Metallic Ferromagnets

Idealized, half-metals have only one spinchannel for conduction: the spin-polarizedband structure exhibits metallic behaviorfor one spin channel, while the other spinband structure exhibits a gap at the Fermilevel. So the density of states at the Fermilevel has, theoretically, 100 % spinpolarization and also the resistance of onechannel goes to infinity. At zero or lowtemperatures, the non-quasiparticle densityof states (electron correlation effects),magnons and spin disorder reduce thepolarization from the idealized 100 %polarization. At higher temperaturesmagnon-phonon coupling and irreversiblecompositional changes affect polarizationfurther.

A special issue presents papers dealingwith some of the crucial issues of HalfMetallic Ferromagnets: J. Phys.: Condens.Matter 19 (2007) Number 31. Somehighlights are briefly summarized here.

Half-Heusler alloyA large international collaboration led byCamelia Borca (Paul Scherrer Institute)presents an extended study of the half-Heusler alloy NiMnSb. They combinedmany experimental techniques and foundthat stoichiometric surfaces exhibit close to100% spin polarization at the centre of thesurface Brillouin zone at the Fermi edge atambient temperatures. They found strongevidence for a moment reorderingtransition at around 80 K which marks thecrossover from a high polarization state to amore representative metallic ferromagneticstate. They found that inducing surfacesegregation by annealing treatments greatlyreduces the surface polarization.

Epitaxial growth and surface propertiesof half-metal NiMnSb filmsC N Borca, D Ristoiu, H-K Jeong, TakashiKomesu, A N Caruso, J Pierre, L Ranno, J PNozières and P A DowbenJ. Phys.: Condens. Matter 19 (2007) 315211(43pp)

Spin polarizationI Galanakis (University od Patras) and PhMavropoulos (Jülich) review some recentresults on the electronic properties of half-metallic Heusler alloys for which the originof the gap and its connection to themagnetic properties are well understood.Changing the lattice parameter slightlyshifts the Fermi level. Spin–orbit couplinginduces states within the gap but the alloyskeep a very high degree of spin polarizationat the Fermi level. Small degrees of dopingand disorder as well as defects with lowformation energy have little effect on the

properties of the gap, while temperatureeffects can lead to a quick loss of half-metallicity.

Spin-polarization and electronicproperties of half-metallic Heusleralloys calculated from first principles I Galanakis and Ph MavropoulosJ. Phys.: Condens. Matter 19 (2007) 315213(16pp)

Material issuesWarren Pickett (University of CaliforniaDavis) and Helmut Eschrig (IFW Dresden)studied the half metallic ferromagnetic statefrom a few different viewpoints. Afteroutlining the formal underpinnings of thespin density functional theory of half metalsthey considered the relativistic effect ofspin–orbit coupling. In principle it destroyshalf metallicity, but in practice it is a minoreffect for the smaller magnetic atoms andeven for heavier atoms, with an appropriatestructure and band filling, a half metal statemay survive.

They also revisited the possibility of a halfmetal with zero net moment, the so-calledhalf metallic antiferromagnet. Althoughthere are several half metals with variousvalues of (integer) moment, there is as yet nogood prospect of a compensated half metalwith M = 0, but there is good reason toanticipate that half metallicantiferromagnets will be discovered. A newkind of superconductivity is possible in suchsystems, somewhat analogous tosuperconductivity in a ferromagnet butwith the minority bands having ‘evaporated’taking their own superconducting gap withthem.

Half metals: from formal theory to realmaterial issuesWarren E Pickett and Helmut Eschrig J. Phys.: Condens. Matter 19 (2007) 315203(10pp)

Spin polarization reaches 100%A G Petukhov (South Dakota School ofMines and Technology) and co-workersshow that the spin polarization of electrondensity in non-magnetic degeneratesemiconductors can achieve 100%. Thiseffect does not require a half-metallicferromagnetic contact and can be realized inferromagnet–semiconductor FM–n+–njunctions even at moderate spin selectivityof the FM–n+ contact when the electronswith spin ‘up’ are extracted from the nsemiconductor through the heavily dopedn+ layer into the ferromagnet and theelectrons with spin ‘down’ are accumulatednear the n+–n interface.

They derived a general equation relatingspin polarization of the current to that of theelectron density in non-magneticsemiconductors and found that the effect ofcomplete spin polarization is achieved nearthe n+–n interface when the concentrationof the spin ‘up’ electrons tends to zero in thisregion while the diffusion current of theseelectrons remains finite.

100% spin accumulation in non-half-metallic ferromagnet–semiconductorjunctionsA G Petukhov, J Niggemann, V NSmelyanskiy and V V OsipovJ. Phys.: Condens. Matter 19 (2007) 315205(16pp)

Calculated total spin moment per unit cell as a function of the total number of valence electrons per unit cell for all the studied half (left panel)and full (right panel) Heusler alloys. The dashed line represents the Slater–Pauling behaviour.

Half metallic ferromagnets are a fundamentally different state of matter with ideally 100% spin polarization







Taming Gd ions in fullerene cages

Water-soluble Gd-based endohedralmetallofullerenes (Gd@C82(OH),Gd@C60(OH), and Gd@C60[C(COOH)10]) arepossible new magnetic resonance imaging(MRI) contrast agents. The toxic Gd ions arecompletely encaged inside the fullerenes,located at an off-centre position within thecage,

A large group headed by R F Sabirianov(University of Nebraska) explored theelectronic properties of Gd@C60 through acomparison of ab initio calculations withphotoemission spectroscopy and resonantphotoemission (constant initial statespectroscopy).

In comparing their calculations based onthe local spin density approximation and theHubbard model description with the

observed photoemission spectra, theyobserved a strong correlation effect, whichmanifests itself in the shift of the Gd 4f stateto higher binding energy, and correlation

energy U of about 7.6 eV, which is larger thannormally detected in gadoliniumcompounds. They attributed that to a lack ofscreening of the encapsulated Gd. Inaddition, they noticed prominent resonantintensity features, due to the Gd 5s and 5pcores in the resonant photoemission spectrataken from 6 eV below the Fermi level, whichindicate strong hybridization between theGd valence states and the fullerene cage. Allthe above phenomena are explained usingthe LSDA + U calculation.

Correlation effects and electronicstructure of Gd@C60

R F Sabirianov et al J. Phys.: Condens. Matter 19 (2007) 082201(6pp)

Encapsulating Gd within C60 enhances its correlation energies

Improvements in electrowetting

When a liquid/liquid interface contacts asolid substrate, applied voltages can causethe interface to change shape. Thiselectrowetting (EW) phenomenon can beapplied in devices requiring no internalmachinery. Also, interfaces in these devicesself-assemble and are difficult to destabilize.Applications include portable lenses,microfluidic devices and electronic displays.

Charles Monroe and Alexei A Kornyshev(Imperial College London) and MichaelUrbakh (Tel Aviv University) propose thatinterfaces between two immiscibleelectrolytic solutions (ITIES), which areimpermeable to ion transfer over a largepotential range, offer immensely betteropportunities for fine shape control at lowvoltages than current EW systems. Also,ITIES can be described by a theoreticalmodel with few free parameters.

Their paper gives full details of a theorythat can be used to describe EW equilibrium.Families of curves are presented to showhow the contact angle between an ITIES andan electrode varies with voltage, to gaugeexpectations for laboratory measurements.They give a detailed analysis of the systemconstruction to illustrate how undesiredartefacts due to experimental geometry canbe avoided. To contrast the case of ITIES,they also give an analysis for systems with acompletely ion-permeable liquid/liquidinterface. Although the latter system is verydifficult to engineer, its comparison to ITIESillustrates the unique features that the ion-impermeability of a liquid/liquid interfaceadds to its EW response.

The distinctive electrowettingproperties of ITIESCharles W Monroe, Michael Urbakh andAlexei A KornyshevJ. Phys.: Condens. Matter 19 (2007) 375113(29pp)

Frieder Mugele and colleagues from theUniversity of Twente report improvementsin conventional electrowetting.

Droplet-based microfluidic research haspotential applications in biochemicalreactions, material synthesis, single-cellanalysis and novel fluid logical devices.Commonly pressure-driven flows are usedto create droplets continuously, providinghigh throughput capability, but it cannotgenerate individual drops on demand norprovide dynamic control of surfacewettability, which can dramatically affect the

dynamics of two-phase microflows.Alternatively, the EW-on-dielectricapproach is used to digitally manipulatedrops, providing exquisite control overindividual drops and surface wettability, butwith low throughput and it cannot readily beintegrated with existing channel-basedtechnologies.

Mugele et al adopt a unified approach tocreate a soft microfluidic platformcombining the advantages of both methods.They incorporate EW into a flow-focusingdevice and demonstrate EW-controlled dropformation. They identify experimentally therange of voltages and driving pressures thatyields EW-induced droplet generation. Atheoretical description based on the balanceof external pressures and voltage-controlledcapillary pressures quantitatively accountsfor the observations. They show that withthis unification the smaller the geometricscales the more efficient the EW control ofdrop generation.

Electrowetting-controlled dropletgeneration in a microfluidic flow-focusing deviceFlorent Malloggi, Siva A Vanapalli, Hao Gu,Dirk van den Ende and Frieder MugeleJ. Phys.: Condens. Matter 19 (2007) 462101(7pp)

A single liquid droplet (d) surrounded by an ambient fluid (s). Both ofthe fluids contact a working electrode (e), and the counterelectrode (c)touches the surrounding fluid only. If ions are dissolved in thesurrounding fluid, a single reference electrode (r), which iselectrochemically reversible to one of the ions, may also be placed inits bulk (far from e, c, and d). In this case a voltage source whichapplies a potential drop between e and c can be used to control thevoltage read by the voltmeter, V.

Interfaces between two immiscible electrolytic solutions offer improved electrowetting

Optimized structure of Gd@C60.






Carbon nanomaterials in biology

Pu Chun Ke and Rui Qiao (ClemsonUniversity) review the problems ofinterfacing nanomaterials, such as carbonnanotubes and fullerenes, with biologicalsystems. They describe ways to improve thesolubility of nanomaterials in aqueoussolutions since, when incorporated intobiological systems, the inert surfacestructures of carbon-based nanomaterialsmay prevent their long-term bioavailabilitydue to aggregation and settlement.

They characterized the diffusion and thecellular delivery of RNA-coated carbonnanotubes using fluorescence microscopy.They simulated translocation of fullerenesacross cell membranes using moleculardynamics to offer new insight into thecomplex issue of nanotoxicity. To assess thefate of nanomaterials in the environment,they discussed the biomodification of lipid-coated carbon nanotubes by the aquaticorganism Daphnia magna.

It is known that the same nanomaterialscan deliver different effects to biologicalsystems, possibly due to physical andchemical modifications to the materials by

biomolecules. Moreover, there is an urgentneed to mitigate nanotoxicity beforenanotechnologies can be developed. Only amultidisciplinary endeavor can ensure thecontinued scientific, environmental, andsocietal development of safe and dependablenanomaterials. The major efforts of physicslie in the experimental detection andtheoretical analysis of the thermal,electronic, and optical properties of

nanomaterials, and in determining theconformational and energetic states ofbiological systems to infer their interaction.Such studies will facilitate the biochemical,biological, and toxicological studies ondeciphering the biological responses tonanomaterials.

New development in advancedmicroscopy and spectroscopy techniques aswell as in atomistic and molecular statisticswill find ample use for such applications.

Carbon nanomaterials in biologicalsystemsPu Chun Ke and Rui QiaoJ. Phys.: Condens. Matter 19 (2007) 373101(25pp)

TEM image of C70–gallic acid complexes.

A multidisciplinary approach is needed to study incorporation of nanomaterials in biological systems

Targeting structures by computation

There is much current interest in problemswhere one inspects large databases ofmolecules or periodic solids in search of astructure with a given target property (e.g.alloy band gap). Such quests often focus onmaterials derived from a given skeletalstructure, the sites of which can be decoratedwith different substituents—chemicalgroups in chemistry and different atoms insolid solutions. In both cases, the sheer sizeof the configurational space can behorrendous.

Mayeul d’Avezac and Alex Zunger of theNational Renewable Energy Laboratorypresent two approaches which identifyeither the minimum-energy configurationor configurations with a target property for afixed underlying Bravais lattice and comparetheir efficiency at locating the deepestminimum energy configuration of facecentered cubic Au–Pd alloy.

In the ‘deepest minimum energyconfiguration search’ finding the exactoptimum decoration suffers nocompromise, whereas in the ‘target propertyconfiguration search’ one is interested intarget structures within a certain range. Inthe case of complex configuration spaceswith many local minima, the more stringentexpectations of the former search require a

global-optimization method such as thereciprocal-space genetic algorithm which isdescribed in the paper. In the latter case, alocal-search method such as the virtual-atom approach, with its ability to directlyfocus on local minima, proves more thanadequate, since the problem can be solvedwithin the first hundred calls to thefunctional for systems up to 48 atoms. Thisputs such studies well within the range ofmore computationally intensive functionalslike density functional theory.

Finding the atomic configuration with arequired physical property in multi-atom structuresMayeul d’Avezac and Alex ZungerJ. Phys.: Condens. Matter 19 (2007) 402201(7pp)

Schematics of (a) the reciprocal-space mating, and (b) the virtual-atom algorithm. In (a) red and blue circles denote the occupation of a latticesite by Au or Pd atoms in the parent configurations P1 and P2. The intermediate offspring configuration Oi is constructed from theconcentration waves (solid lines) of AuPd material present P1 and P2, i.e. from their structure factors. A physical configuration is obtained via anormalization step. The virtual atom (b) implements a local-search method where the decision to explore a neighboring discrete configurationis deduced from the gradient at the original discrete configuration.

New techniques to compute a structure with a target property are more efficient





Monitoring biomolecular interactions

The novel characteristics of nanomaterialsenable highly sensitive and specificapplications in electronics, optics andbiotechnology. In particular, nanomaterialshave become the preferable tools formonitoring biomolecular interactions on abiochip without labelling procedures usingenzymes and fluorescent dyes.

A Japanese group led by Tatsuro Endo ofthe Tokyo Institute of Technology used alocalized surface plasmon resonance (LSPR)label-free biochip constructed with acore–shell structured nanoparticle layersubstrate for the label-free detection ofPNA–DNA and DNA–DNA hybridizationreactions. PNA (peptide nucleic acid) andDNA probe immobilized LSPR label-freebiochips are promising candidates for thespecific detection of target DNA.

The LSPR label-free biochip is easy tofabricate, and the apparatus cost for theoptical characteristics evaluation issignificantly lower than that of aconventional SPR apparatus; also, theoperation procedure has become moreconvenient, without any labellingprocedures. Moreover, the core–shell

structured nanoparticle layer substrate coulddetect low concentrations of target DNA.From these advantages, they concluded thatthe novel characteristics of their substratethat could excite LSPR is more suitable formonitoring biomolecular interactions thanthe conventional LSPR-based biochipsreported previously. Certainly, the LSPR-based label-free optical monitoring methodpromises to offer a massively paralleldetection capability in a highly miniaturizedpackage.

Excitation of localized surface plasmonresonance using a core–shell structurednanoparticle layer substrate and itsapplication for label-free detection ofbiomolecular interactionsTatsuro Endo, Kagan Kerman, NaokiNagatani and Eiichi TamiyaJ. Phys.: Condens. Matter 19 (2007) 215201(10pp)

Experimental procedure using the LSPR label-free biochip.

Nanomaterials offer an ideal tool to monitor biomolecular interactions on a chip

Simulating charge transport in ion channels

Biological ion channels have importantpharmaceutical and engineeringapplications. Simulating charge transport inion channels is a challenging problem.Predicting the electro-physiology of ionchannels requires reliable modelling of eachsubsystem: the channel protein itself, themembrane within which the channel isinserted, and the electrolyte solution bathingthe system. The simulation of eachcomponent presents its own challenges andthe simulation is further complicated by thecharacteristic time and space scale of the ionchannel system. The transit time of charge inion channels is typically nanoseconds, whilethe time resolution required to represent theionic motion is in the femtosecond range.Likewise, the entire system has a nanometresize, while the particle trajectories have to beresolved within a fraction of an angstrom. Acomputer model needs to describe thesystem very accurately in both time andspace, for a relatively long simulation time inorder to extract reliable transport properties.

David Marreiro (Illinois Institute ofTechnology) and colleagues studied thesuitability of a P3M force field scheme

coupled with a Brownian dynamicssimulation engine for the accurate modellingof charge transport in ion channels by testingthe relative importance and influence ofcritical model parameters such as thedielectric representation and the parametersgoverning the ion dynamics. They comparedthe results with published experimental andsimulated data, and found that a carefulchoice of the model parameters yields anefficient and accurate model for chargetransport in porin channels. They alsoproposed a way to improve this model whilemaintaining its computational advantage.

Brownian dynamics simulation ofcharge transport in ion channelsDavid Marreiro, Marco Saraniti and ShelaAboudJ. Phys.: Condens. Matter 19 (2007) 215203(16pp)

These papers are part of a special section onMolecular and Bio Electronics, J. Phys.: Condens.Matter 19 Number 21.

The OmpF porin channel from E. Coli, embedded in an explicit POPC membrane (left), and the corresponding top view of the OmpF alone(right).

Charge transport in ion channels has been accurately simulated





Spinel taps rich vein of properties

Spinel compounds are very widely used, e.g.in magnetic recording media, batteries,catalysts and pigments. They occur asnatural minerals and are important ingeophysics, e.g. for palaeomagneticreconstructions of the drifting continents.

Their physical properties depend cruciallyon the distribution of cations betweentetrahedral (A) and octahedral (B) sites. C MB Henderson and colleagues at ManchesterUniversity have carried out a systematicstudy of the cation distribution in ferritespinels using K-edge x-ray absorptionspectroscopy (XAS). Their samples includednatural and synthetic end-membermagnetites, a natural Mn- and Zn-richmagnetite, and synthetic binary, ternary andquaternary ferrites M2+O·M3+

2O3, where M2+

= Mg, Co, Ni, Zn and M3+ = Fe, Al. Theyobtained XAS data for all metals. Complete,unfiltered, EXAFS spectra were refined todetermine the percentage distribution ofeach element over the A and B sites and thesedata were combined with microprobeanalyses to quantify the tetrahedraloccupancy for each element in each sample.

They used measured site occupancies andan internally consistent set of (M–O)A and(M–O)B bond lengths to calculate unit-cell

parameters, which showed excellentagreement with measured values. Theyfound that the order of increasing tendencyto order into tetrahedral sites in ferrites isFe2+ < Ni < Al < Co < Mg = Mn < Zn. Thetetrahedral occupancy factor for Fe3+ coversa wide range (0.92–0.19), suggesting that Fe3+

plays a relatively passive role and merelymakes good any deficit in the A site.

Cation occupancies in Mg, Co, Ni, Zn, Alferrite spinels: a multi-element EXAFSstudyC M B Henderson, J M Charnock and D APlantJ. Phys.: Condens. Matter 19 (2007) 076214(25pp)

The main control of pre-edge peak intensity is the amount of Fe3+ intetrahedral coordination, as Fe3+ and Fe2+ have similar and smallerpre-edge peak intensities for octahedral coordination. The figuresuggests that the pre-edge data are in reasonable agreement with thesite occupancies for Fe3+ determined from the EXAFS data.

EXAFS has been used to carry out a comprehensive study of ferrite spinels

Improved simulation of water

Water is the most important natural solvent,both for biological function and technicalprocesses, so aqueous solutions are amongthe most studied systems. However, bothexperiments and theoretical models areusually restricted to specific cases. Inparticular all-atom simulations ofbiomolecules and materials in water arecomputationally very expensive and oftennot possible, mainly due to thecomputational effort to obtain water–waterinteractions in regions not relevant for theproblem under consideration. Luigi Delle Site of Max-Planck-Institute forPolymer Research, Mainz, and colleagues atRice University present a coarse-grainedmodel that can reproduce the behaviour ofliquid water at a standard temperature andpressure remarkably well. They use thismodel in a multiscale simulation of liquidwater, where a spatially adaptive molecularresolution procedure allows one to change

from a coarse-grained to an all-atomrepresentation on-the-fly. They show thatthis approach leads to the correctdescription of essential thermodynamic andstructural properties of liquid water. Thisadaptive multiscale scheme allows for

significantly greater extensive simulationsthan existing approaches by taking explicitwater into account only in the regions wherethe atomistic details are physically relevant.Such a multiscale resolution of water isexpected to play an important role in themodelling of wet/dry interfaces and inbiomolecular simulations. The gain incomputational speed will allow for largersystems and more systematic studies andshould at the same time extend thepossibilities of such simulations to a largeruser group.

Adaptive resolution simulation of liquidwaterMatej Praprotnik, Silvina Matysiak, LuigiDelle Site, Kurt Kremer and Cecilia ClementiJ. Phys.: Condens. Matter 19 (2007) 292201(10pp)

On-the-fly interchange between the all-atom and coarse-grainedwater models. Top: the explicit all-atom water molecule is representedat the right, and the coarse-grained molecule at the left. The middlehybrid molecule interpolates between the two (see text). Bottom: aschematic representation of the full system, where a hybrid regionconnects the explicit and coarse-grained levels of description.

Multiscale simulation of water gives an accurate description of its properties





Crystals under anisotropic stress

The equilibrium properties of crystals showsubstantial change when they are subjectedto stress. Hydrostatic pressure produceslarge changes in structure, elastic responseand stability, including discontinuouschanges to new phases. First-principlesband-structure programs account well forthese properties, but the effects ofanisotropic stress introduce complicationsand have not been accounted for.

P M Marcus and F Jona (SUNY) describe afirst-principles calculation procedure fordetermining the structure, elastic responseand stability of a crystal in equilibrium underanisotropic stress. They showed that under astrain the change in internal energy plus thework done by the crystal is a minimum withrespect to structural changes, and can beexpanded in powers of the Eulerian strains.They showed that the coefficients of second-order terms in the expansion are effectiveelastic constants for the equilibrium crystal

which determine stability. They applied the method to body-centered

tetragonal (bct) Al to evaluate the latticeparameters as functions of lateral andlongitudinal stresses. They found two stablebct phases at a given longitudinal stress, onewith the lateral stress mainly larger and onewith lateral stress smaller than the

longitudinal stress. They established thestability of the structure in each of these bctphases by showing that all the eigenvalues ofthe effective elastic constant matrix arepositive.

Structure and stability of crystals underanisotropic stressP M Marcus and F JonaJ. Phys.: Condens. Matter 19 (2007) 436208(12pp)

Lattice parameters c of bct Al as functions of transverse stress -�1

when the longitudinal stress -�3 is held constant and equalt to thepressure, p = 0, 600, 1200, 1840 kbar,

A new method accounts for the effects of anisotropic stress on the structure and stability of crystals

Nucleation in soft matter

Richard Sear (University of Surrey) reviewswork on nucleation: the process which startsoff a first-order phase transformation. Hereviews theoretical and simulation work onboth homogeneous and (especially)heterogeneous nucleation. He considersboth general aspects and those specific toprotein solutions and colloidal suspensions.

In one very simple system, monodispersehard spheres, nucleation is fairly wellunderstood. Computer simulation results forhomogeneous nucleation agree withexperiment to within a couple of orders ofmagnitude. Also, heterogeneous nucleationat a hard wall has been shown to be orders ofmagnitude faster than homogeneousnucleation. Thus monodisperse hard spheresin a container with hard walls should freezefrom the outside in.

In protein solutions, a much morecomplex system, nucleation is still not wellunderstood. Even for lysozyme, the moststudied protein, there is an ongoing debateabout whether the observed nucleation ishomogeneous or heterogeneous. The role ofimpurities is obscure, although lysozyme

dimers affect the nucleation rate, anddisordered porous media induce nucleationin solutions where the high nucleationbarrier would otherwise precludenucleation.

Future progress will require quantitativeexperimental studies of nucleation rates,experimental studies in which nuclei areimaged, and detailed simulation studies. Inthe experimental studies, care should be

taken to determine whether the nucleation ishomogeneous or heterogeneous. Forexample, if adding or removing impuritiesalters the nucleation rate then it must beheterogeneous.

Unfortunately, clearly demonstrating thatthe nucleation is homogeneous is harder.

Nucleation: theory and applications toprotein solutions and colloidalsuspensionsRichard P SearJ. Phys.: Condens. Matter 19 (2007) 033101(28pp)

Schematic diagrams of critical nuclei in the bulk, on a flat surface, ina 90º corner or wedge, and in a slit pore. The first three are nuclei of anew bulk phase and are at the same value of the supersaturation. Thenucleus for homogeneous nucleation is a sphere, whilst those forheterogeneous nucleation on flat surfaces and in wedges are parts ofspheres of the same radius.

Theory of nucleation in protein solutions and colloidal suspensions is reviewed





Ferromagnetic double perovskites

There has been much recent interest in half-metallic ferromagnets such as Sr2FeMoO6

because of their potential application inspintronics. J M De Teresa and co-workersfrom Zaragoza present a comprehensivereview of the structural, magnetic andtransport properties of double perovskites(A2BB’O6) with ferromagnetism above roomtemperature. Ferromagnetism in thesecompounds is explained by an indirectB–O–B’–O–B exchange interaction mediatedby itinerant electrons.

The BB’ = FeMo-based double perovskites,of which Sr2FeMoO6 (TC = 420 K) is the moststudied, show metallic behaviour and lowmagnetic coercivity.

In the B’ = Re compounds, the significantorbital moment of Re plays a crucial role inthe magnetic properties, for example in thelarge magnetic coercivity andmagnetostructural coupling. The A2FeReO6

series, with maximum TC = 520 K forCa2FeReO6, shows a tendency tosemiconducting behaviour. Finally, theSr2(Fe1-Cr )ReO6 series, of which Sr2CrReO6

has the highest known TC in an oxidecompound without Fe(625 K) and is metallic.

The authors discuss the impact of thesematerials for spin electronics in the light oftheir high spin polarization at the Fermi leveland metallicity. There is particular interest inthe large intergrain magnetoresistance effectobserved in polycrystalline samples and thepossible implementation of these materials

as electrodes in magnetic tunnel junctions.Further challenges are to develop growthroutes for thin films and single crystals, inorder to realize breakthrough spintronicdevices.

Double perovskites withferromagnetism above roomtemperatureD Serrate, J M De Teresa and M R IbarraJ. Phys.: Condens. Matter 19 (2007) 023201(86pp)Phase diagram of A2FeMoO6 with data taken from several

references The solid line is the averaged value of TC. Dark areascorrespond to the ferromagnetic phase, while lighter ones to theparamagnetic phase.

Double perovskites show a range of magnetic and transport properties with potential device applications

How wetting affects drying

Porous materials such as concrete in contactwith the air undergo imbibition–dryingcycles which seriously affect their durability.Hydrophobic surface treatments reduce thedamage by creating a protective layerpreventing water from imbibing the porousmedium. However, the effect of wettabilityon water transport within porous media isnot well understood.

N Shahidzadeh-Bonn, A Azouni and PCoussot at the Institute Navier, France havecarried out drying experiments on modelporous media with well controlledwettability properties of the solid. They alsovaried the boundary conditions by allowingthe presence or absence of air flow at theevaporating surface.

For a hydrophilic porous medium, dryingis mainly controlled by the liquid filmcovering the solid grains and capillary riseinside the pores, leading to a constant dryingrate and a homogeneous desaturation of thewhole sample in time. The evaporationkinetics of a hydrophobic porous medium isslower because of the small capillary riserelated to the wetting heterogeneities(partially wetted surface). If the evaporatedsurface is no longer wetted by the liquid

(corresponding to a receding drying front),the evaporated molecules have to betransported by a diffusion process.

A surprising result of the competitionbetween localized capillary rise anddiffusion is that over long times theevaporation rate can become smaller with airflow that without. Due to air flow, the initialdrying rate at the surface is large andcapillary transport remains insufficient to

maintain liquid at the evaporating surfaceand hence ensure a partially wetted medium.Consequently, drying becomes governed bydiffusion only associated with a receding(dry) front.

Effect of wetting properties on thekinetics of drying of porous mediaN Shahidzadeh-Bonn, A Azouni and PCoussotJ. Phys.: Condens. Matter 19 (2007) 112101(7pp)

Evaporated mass of liquid as a function of time for a hydrophobicporous medium (a) without air flow and (b) in the presence of an airflow on the top surface (0.2 m s -1).

Surprisingly, air flow can reduce the rate of drying of a hydrophobic porous medium





Spin ices get stuffing

In ‘spin ices’ exchange interactions, crystalfields, and dipolar interactions are in adelicate balance, yielding a ground state withlarge residual spin entropy. ‘Stuffed’ spin iceshave shown that an increase of the density ofspins results in very little change in theresidual entropy, so residual entropy statesmight be relatively common.

Jason Gardner (NIST) together withworkers at the National High Magnetic FieldLaboratory and others have performed onscattering experiments on a crystal of stuffedspin ice Ho2.3Ti1.7O7-�, to observe how thespins order at low temperatures. This systemstill has some key signatures of the spin icestate, but the spin dynamics is significantlyaltered.

The excess residual entropy/spin can beexplained through the remaining fluctuatingHo3+ spins upon the B-sites that do notfollow the ice rules. These spins shift thecorrelations of the ice state on the A-site to aferromagnetic character, and this newground state is more dynamic that thetradition ‘frozen’ ice state.

‘Stuffing’ the system with extra spins

seems to free up the dynamics. The oppositeapproach, adding diamagnetic impurities tothe system, has been predicted to have thiseffect much like doping water ice with KOHleads to new ordered phases. ‘Stuffing’lattices with extra spins might yield a similarresult, leading to new magnetic phases athigher doping levels.

It is possible that the new modes in the‘stuffed spin ice’ are from collective modes ofa more dynamic ice system as a whole, whichwould be expected to be ergodic, with no

residual entropy. The realization of the spinliquid within the ‘stuffed spin ice’ (in effect,melting the ice state through the increaseddensity of spins) would seem to violate thethird law of thermodynamics.

The origin of persistent spin dynamicsand residual entropy in the stuffed spinice Ho2.3Ti1.7O7-�

H D Zhou et al J. Phys.: Condens. Matter 19 (2007) 342201(7pp)

Inelastic neutron scattering experiments on the x = 0.3 stuffed spin ice at 55 mK, 700 mK and 10 K, noting the appearance of a gapped spinexcitation at low temperatures.

Stuffing spin ices with extra spins appears to lead to new magnetic phases

Image: Artistic impression of coordination of atoms on a chiral surface of copper A Kara and T Rahman 2006 Journal of Physics: Condensed Matter 18 8883–8890

WORKING TO PUBLISH THE BEST IN

If your research is within fundamental condensed matter science, including soft matter and nanostructures, the Editorial board would be delighted to invite you to submit your work.

Visit www.iop.org/journals/authorsubs to submit your paper today.

FAST TRACK YOUR RESEARCH

FTCs will be refereed by a member of the Editorial Board who will check that they have the necessary urgency, processed quickly and made freely available for everyone to read in the electronic journal.

For more information, including full author guidelines, visitwww.iop.org/journals/jpcm, or email us at [email protected].

Condensed Matter

Fast Track Communications (FTCs): we welcome shortpapers of the most outstanding quality that report new andtimely developments in condensed matter physics.


PUBLISHED BYIOP P UBLISHING Journalof Physicsej.iop.org/pdf/jpcm/2007_top_papers.pdf · PUBLISHED...

Documents

Transcript of PUBLISHED BYIOP P UBLISHING Journalof Physicsej.iop.org/pdf/jpcm/2007_top_papers.pdf · PUBLISHED...