ry n - National Center for Theoretical Sciences, Physics · 2015. 4. 14. ·...
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Transcript of ry n - National Center for Theoretical Sciences, Physics · 2015. 4. 14. ·...
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International Workshop on Quantum Control of Electrons on Liquid Helium and Other Low-‐Dimensional Systems
December 15–16, 2014
Lecture Room 353, Science Building III, National Chiao Tung University (交通大學基礎科學大樓)
December 15 (Monday) 09:00 – 09:20
Registration Title of talk
Chair: Prof. Juhn-‐Jong Lin (NCTU)
09:20 – 09:30
Prof. Juhn-‐Jong Lin (NCTU)
Opening
09:30 – 10:00
Prof. Kimitoshi Kono (RIKEN)
An Introduction to Electrons on Helium
10:00 – 11:00
Prof. Steve Lyon (Princeton University)
Mobile Spin Qubits: Silicon ICs meet Superfluid Helium
11:00 – 11:20
Coffee break
Chair: Dr. Kostya Nasyedkin (RIKEN)
11:20 – 12:20
Prof. Tse-‐Ming Chen (NCKU)
Spin-‐orbit Coupling and the Realization of Spin Transistors
12:20 – 14:00
Lunch
Chair: Dr. Shao-‐Pin
Chiu (NCTU)
14:00 – 15:00
Niyaz Beysengulov (RIKEN)
Influence of Confinement on the Melting of Quasi-‐1D Wigner Crystals
15:00 – 15:30
Prof. Jiunn-‐Yuan Lin (NCTU)
Coexistence of Ferromagnetism and d-‐wave superconductivity in YBa2Cu3O7-‐x/ La0.7Ca0.3MnO3 bilayer
15:30 – 15:50
Coffee break
Chair: Dr. Yu-‐Chen Sun (RIKEN)
15:50 – 16:50
Dr. Alexander Badrutdinov (OIST)
Hysteretic Transport Properties of Surface Electrons on Helium in Quasi-‐1D Geometry
16:50 – 17:20
Dr. Petr Moroshkin (RIKEN)
Laser Spectroscopy of Ba+ Ions in Superfluid He
18:30 – 20:30
Banquet
December 16 (Tuesday) Speaker Title of talk Chair:
Dr. Kimitoshi Kono (RIKEN)
09:00 – 10:00
Prof. Francois Peeters (University of Antwerp)
Correlated Electrons in Nanostructured Systems
10:00 – 10:30
Chun-‐Shuo Tsao (NCTU)
A New Type of Structural Transition in a Quasi-‐One-‐Dimensional Wigner Crystal
10:30 – 10:50
Coffee break
Chair: Dr. Sheng-‐Shiuan Yeh (NCTU)
10:50 – 11:40
Prof. Denis Konstantinov (OIST)
Magneto-‐transport in Electrons on Helium under Cyclotron-‐Resonance Excitation
11:40 – 12:10
Dr. Leonid Abdurakhimov (OIST)
Microwave Study of Surface Electrons on Liquid Helium in a Fabry-‐Perot Cavity
12:10 – 13:30
Lunch
13:30 – 15:00
Lab tours and free discussion
15:00 – 21:00
Excursion to Hakka village
An introduction to electrons on helium
K. Kono1,2
1RIKEN CEMS, Japan, 2NCTU, Taiwan
Surface state electrons (SSE) on liquid helium have been studied since early 70s.
This system is one of the cleanest low dimensional electron systems. The SSE
have their solid-‐state counterparts in MOSFETs, quantum wires, quantum dots,
and so on. One can find much similarity between the SSE and the counterparts. I
will describe a brief overview of the SSE, in particular, from the dimensionality
viewpoint.
Mobile Spin Qubits: Silicon ICs meet Superfluid Helium
S. Lyon
Princeton University, U.S.A.
There has been a great deal of interest over the last decade in developing a
technology for constructing quantum information processors. Devices which
operate on quantum bits (or qubits) are so different from conventional classical
devices that approaches from almost all branches of physics are being
considered. However, it is also becoming clear that a useful quantum computer
will require at least thousands and probably millions of qubits and quantum
gates. That realization is driving many schemes to find a way to utilize
semiconductor technology for scaling. One approach which maps almost
perfectly onto silicon technology is to use electrons floating on the surface of
superfluid helium as spin qubits. Starting from a conventional CMOS foundry
process, specially designed and processed silicon ICs have been used to
transport electrons across a helium surface. Charge coupled devices with
essentially perfect charge transfer efficiency have been demonstrated, down to
the level of one electron per pixel. These and related experiments will be
discussed, as well as some of the challenges which lie ahead for developing a full
quantum device technology.
Spin-‐orbit coupling and the realization of spin transistors
T.-‐M. Chen
National Cheng Kung University, Taiwan
The spin field effect transistor (FET) envisioned by Datta and Das opens a
gateway to spin information processing. Although the coherent manipulation of
electron spins in semiconductors is now possible, the realization of a functional
spin FET for information processing has yet to be achieved, owing to several
fundamental challenges such as the low spin-‐injection efficiency due to
resistance mismatch, the spin relaxation, and the spread of spin precession
angles. Here I will review the recent advances in this field and present our
contributions to the realization of spin FETs.
Influence of Confinement on the Melting of Quasi-‐1D Wigner Crystals
N. R. Beysengulov 1,2 1RIKEN CEMS, Japan, 2Kazan Federal University, Russia
The melting of many-‐body systems in constricted geometries is of
importance in a wide range of research areas, such as cold atoms, colloids,
quantum wires and carbon nanotubes. For a particular system, the
mechanism of melting depends on the interaction between the particles
that form the crystal lattice, leading to an inability to build a general
theory of solid-‐liquid phase transitions. However, a detailed microscopic
description of melting in two dimensions (2D) based on the dissociation of
pairs of topological defects close to the melting point has been developed
by Kosterlitz and Thouless, and Halperin, Nelson and Young (KTHNY
theory). Here we present transport measurements of a model Coulomb
system, electrons trapped on the surface of liquid helium, in a
microchannel with fully controllable confinement parameters. We
demonstrate that the electron transport is uniquely sensitive to the
particle ordering, which allows us to investigate the melting of the electron
lattice whilst continuously varying the system dimensionality, from the
quasi-‐2D case to the limit of the single electron chain. By controlling both
the particle density and the effective width of the microchannel we
determine a phase diagram for the quasi-‐1D electron system. We find that
the phase boundary between the electron liquid and Wigner crystal states
exhibits a series of fringes, each corresponding to a commensurate state of
the electron lattice with the confinement geometry. This allows us to count
the number of electron rows formed in the microchannel. We find that the
melting is suppressed with increasing confinement, with the interelectron
spacing at melting for the single chain much larger than in the 2D case. Our
results can be compared with other classical or quantum phase transitions
in confined geometry.
Coexistence of ferromagnetism and d-‐wave superconductivity in YBa2Cu3O7-‐x/ La0.7Ca0.3MnO3 bilayer
J.-‐Y. Lin1,2, Shih-‐Wen Huang2, 3, L. Andrew Wray1, Horng-‐Tay Jeng4, 5, V. T. Tra1, J. M. Lee6, M. C. Langner3, J. M. Chen6, S. Roy2, Y. H. Chu5,7, R. W. Schoenlein3, and Yi-‐De Chuang2 1Institute of Physics, National Chiao Tung University, Hsinchu 30010, Taiwan 2Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA 3Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA 4Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan 5Institute of Physics, Academia Sinica, Taipei 11529, Taiwan 6National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan 7Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan Ferromagnetism and d-‐wave superconductivity are often regarded as
incompatible to each other. With no crystalline materials showing the
coexistence of these two orders, studying their mutual interactions remains
restrictive to date. However, such studies can be performed on
cuprate/manganite heterostructures where these two orders are brought into
proximity. Here we show the coexistence of ferromagnetism and d-‐wave
superconductivity in bulk superconducting YBa2Cu3O7-‐x (YBCO) grown on top of
ferromagnetic La0.7Ca0.3MnO3 (LCMO). The coexistence is present with MnO2
interfacial termination, but absent with La0.7Ca0.3O interfacial termination. The
difference originates from distinct energetics of CuO chain and CuO2 plane next
to LCMO layer at these two interfaces such that the spin-‐polarized electrons
transferred from manganites to cuprates are influenced differently. As such, the
ferromagnetic coupling inside YBCO layer can be sustained by the enhanced
double-‐exchange interaction. Our findings demonstrate the far-‐reaching impacts
of interfacial interactions to bulk physical properties, and open up a new
paradigm of using nanoscale heterogeneity to study the competing quantum
orders in correlated electron systems.
Hysteretic transport properties of surface electrons on helium in quasi-‐1D
geometry
A. Badrutdinov
Okinawa Institute of Science and Technology, Japan
We report about recent experiments where transport properties of surface
electrons on helium in quasi-‐1D geometry have been studied. We have found
that the current of surface electrons through a long channel has a strongly
hysteretic dependence on temperature below 0.5 K. Upon cooling down a
pronounced minimum of the current is observed at about 20 mK. Upon warming
up the current is suppressed in a broad temperature range up to 0.5 K. In the
range of suppression the current either drops to zero, or develops an unstable
behavior, characterized by an increased noise and occasional fluctuations. The
phenomenon is sensitive to the potential in the channel, indicating importance of
the confinement. Preliminary analysis suggests that formation of the self-‐trapped
(polaronic) state of surface electrons might be relevant.
Laser spectroscopy of Ba+ ions in superfluid He
P. Moroshkin1, R. Batulin1,2, K. Kono1
1RIKEN CEMS, Japan, 2Kazan Federal University, Russia
Free electrons and He+ ions trapped at the surface of liquid He represent a model
two-‐dimensional electronic system that is widely used in experiments. They also
serve as probes for the properties and excitations of the free surface of the
superfluid. Much less is known about the properties of foreign atomic ions
interacting with the liquid He surface. In contrast to free electrons and He+ ions,
the ions of various metallic elements can be observed and manipulated by
methods of laser spectroscopy that offers exciting new perspectives for the
entire field of 2D electronic systems at liquid He surfaces.
Recently, we have proposed [1] to trap Ba+ ions under the surface of
superfluid He and use their spins as a probe for surface excitations. It is expected
[2] that in superfluid 3He-‐B the relaxation of the spins may depend on their
initial orientation with respect to the surface. Such dependence would indicate
the existence of a quasiparticle possessing the properties of Majorana fermion.
In my talk, I will discuss the properties of impurity ions embedded in
superfluid He and present our recent experiments on the injection of Ba+ ions in
superfluid 4He and their detection by the methods of laser spectroscopy.
[1] R. Batulin et al., J. Low Temp. Phys. 175, 63 (2014)
[2] S. B. Chung, S. C. Zhang, Phys. Rev. Lett. 103, 235301 (2009)
Correlated electrons in nanostructured systems
F. M. Peeters
Departement Fysica, Universiteit Antwerpen, B-‐2020 Antwerpen, Belgium
Using Monte Carlo techniques, molecular dynamics simulations and analytical
approaches, correlation between particles in nanostructured systems were
investigated. The possible ordered structures and phase transitions between
them were investigated. For example, a Mendeleev-‐type table for classical atoms
was obtained and a phase diagram for quasi-‐one-‐dimensional confined systems.
The latter exhibits a remarkable lane formation where with increasing density
the following ordering of lanes was found: 1 à 2 à 4 à 3 à 4 à 5 à ….
The diffusion of particles confined into wire-‐like structures were studied. At low
density single file diffusion behaviour is found with its typical time dependence.
With increasing particle density a smooth transition from 1D to 2D diffusion
occurs. The presence of a periodic potential along the wire has an impact on this
diffusive behaviour.
A local constriction along the wire pins the correlated state of the particles. We
found that friction together with the constriction pins the particles up to a
critical value of the driving force. The system can depin elastically or
quasielastically depending on the strength of the constriction. The elastic-‐
quasielastic depinning is characterized by a critical exponent. The dc
conductivity is zero in the pinned regime, it has non-‐Ohmic characteristics after
the activation of the motion and then it is constant. Furthermore, the
dependence of the conductivity with temperature and strength of the
constriction was investigated in detail. We found interesting differences between
the single-‐chain and the multichain regimes as temperature is increased.
The above classical systems exhibit a rich amount of physics which illustrate
basic concepts in solid state physics. Presently, several experimental realizations
of such a classical system exists: colloidal particles, dusty plasma’s, electrons on
liquid helium, little metallic balls between two condensator plates, quantum dots
in high magnetic fields, …
A new type of structure transition in quasi-‐one-‐dimensional Wigner crystal
C.-‐S. Tsao
National Chiao Tung University, Taiwan
We studied theoretically the properties of a quasi-‐one-‐dimensional Wigner
crystal of charged particles. Following the study by Peeters group, we obtained
the ground state structure as a function of the linear density up to 20-‐row
structure. It is already pointed out that the number of chains grows as
1à2à4à3à4à5à6…, as we increase the density. The transition from 2 to 4 is
attributed to so called the “zig-‐zag” transition. Except this irregular transition,
the number of chains is believed to increase by one. In our study, we found that
there exists another irregular transition 8à13 in a high density regime. We
discuss the structural change and the melting behavior around the density at
which this new irregular transition takes place. We also examine the possible
correspondence between the irregular transition and a recent experiment by
Rees.
Magneto-‐transport in electrons on helium under cyclotron-‐resonance
excitation
D. Konstantinov
Quantum Dynamics Unit, OIST Graduate University, Okinawa, Japan
Recently there has been a surge of interest in magneto-‐transport phenomena in
two-‐dimensional (2D) electron systems subjected to perpendicular magnetic
field and electro-‐magnetic radiation. In particular, microwave-‐induced resistance
oscillations and zero-‐resistance states (ZRS) has been observed in high-‐mobility
semiconductor heterostructures and in 2D electrons on liquid helium [1,2]. It is
believed that in both systems electrons are driven into ZRS state by instability of
a negative-‐dc-‐conductivity state.
Cyclotron resonance of 2D electrons provides one of the well understood
examples of resonant interaction between electro-‐magnetic radiation and a
system of charged carriers. However, its effect on carrier transport can be very
non-‐trivial. Typically, the cyclotron excitation causes only transitions between
adjacent Landau levels, and the cyclotron resonance induces strong overheating
of the electron system as photo-‐excited electrons climb up the equidistant
Landau energy spectrum. Our recent study of electrons on helium under
cyclotron resonance excitation showed an unusually large expansion of the
electron system in a lateral direction, which is hard to understand in the
conventional framework of the effective electron temperature approximation
[3]. Recently, it has been suggested that photon-‐assisted scattering can lead to
negative absolute conductivity and associated with it instability of the electron
system under cyclotron-‐resonance excitation, which could explain this usually
large expansion of the electron system [4]. We analyze our experimental data in
the framework of the proposed theory and consider possibility for such
instability.
[1] R. Mani et al. Nature 420, 646 (2002); I. A. Dmitriev et al. Rev. Mod. Phys. 84, 1709 (2012). [2] D. Konstantinov, K. Kono, Phys. Rev. Lett. 105, 226801 (2010). [3] A. O. Badrutdinov, L. V. Abdurakhimov, D. Konstantinov, Phys. Rev. B 90, 075305 (2014). [4] Yu. P. Monarkha, private communication.
Microwave study of surface electrons on liquid helium in a Fabry-‐Perot
cavity
L. Abdurakhimov, W. Powell, D. Konstantinov
Okinawa Institute of Science and Technology, Japan
We report preliminary results of microwave absorption measurements in two-‐
dimensional electron system on the surface of superfluid helium-‐4. To enhance
measurement sensitivity, experiments were performed in a horizontally oriented
Fabry-‐Perot cavity consisted of two copper spherical mirrors. Surface electrons
were placed near the axis of the cavity. In consistence with the previous
experiments, two features of surface-‐state electron microwave absorption were
observed. When the electron layer was placed far enough from the cavity axis,
absorption peak had an asymmetric shape. When the surface of liquid helium
was close to the axis, the absorption spectrum had multiple-‐peak structure.
Also, in microwave studies of the liquid helium surface without electrons, it was
observed that microwave power reflected from the cavity was oscillating with
time when the experimental cell was subjected to mechanical vibrations. We
suppose that observed sensitivity to mechanical oscillations can be caused by
coupling between surface waves on liquid helium and microwave radiation
inside the Fabry-‐Perot resonator.
Offices for Workshop Participants Office space is available on the 4th floor for those participants visiting from overseas. Your room number is listed below. If you would like to use your office, please ask the organisers for the key. Room Dates Name Affiliation 415.1 15-‐19 Dec Petr Moroshkin RIKEN, Japan 415.2 15-‐19 Dec Kostya Konstantin RIKEN, Japan 417 15-‐17 Dec Denis Konstantinov OIST, Japan 418.1 15-‐20 Dec Niyaz Beysengulov RIKEN, Japan 418.2 15-‐20 Dec Yu-‐Chen Sun RIKEN, Japan 419 15-‐17 Dec Alexander Badrutdinov OIST, Japan 420 15-‐17 Dec Francois Peeters University of Antwerp 421.1 15-‐17 Dec William Powell OIST, Japan 421.2 15-‐17 Dec Jui-‐Yin Lin OIST, Japan 422 11-‐17 Dec Steve Lyon Princeton, U.S.A. 426 15-‐28 Dec Kimitoshi Kono RIKEN, Japan 430 15-‐17 Dec Leonid Abdurakhimov OIST, Japan
