FLORIDA STATE UNIVERSITY · UNIVERSITY OF FLORIDA · LOS ...Lab as a principal investigator . In...

VOLUME 17 • NO. 2SPECIAL EDITION

N AT I O N A L H I G H M AG N E T I C F I E L D L A B O R ATO RY

F LO R I D A S TAT E U N I V E R S I T Y · U N I V E R S I T Y O F F LO R I D A · LO S A L A M O S L A B

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tS 4 . . . IntroductionfromtheDirector

6 . . . Education,OutreachandDiversity

COnDEnsEDMattErPhysICsGraphene, Basic Superconductivity, Other Condensed Matter, Qubits & Quantum Entanglement, Quantum Fluids & Solids, Condensed Matter Technique Development, Magnetism & Magnetic Materials

8 . . . symmetryBreakingoftheZeroEnergyLandauLevelinBilayerGraphene

9 . . . Many-bodyInstabilityofCoulombInteractingBilayerGraphene

10 . . Pronouncedhalf-IntegerQuantumhallEffectonEpitaxialGrapheneupto70K

12 . . halfIntegerQuantumhallEffectinhighMobilitysingleLayerEpitaxialGraphene

13 . . CyclotronresonanceattheChargeneutralPointofGraphene

14 . . WhatCanWeLearnfromtheangle-dependenceofQuantumOscillationsinyBa2Cu

3O

6+x?

16 . . LandauLevelPhysicsinanUnderdopedhightemperaturesuperconductoryBa2Cu

3O

6 .56

17 . . highFieldspecificheatofUltracleanyBCO6 .55

:CoexistingFermiLiquidandd-wavesuperconductingGap

18 . . topologicalChangeoftheFermisurfaceinternaryIronPnictideswithreducedc/a ratio:adehaas–vanalphenstudyofCaFe

2P

2

19 . . MagneticOrderingoftheRElatticeinREFeasO:theOddCaseofsm .aspecificheatInvestigationinhighMagneticField

20 . . InterplayofFrustrationandMagneticFieldforthe2DQuantumantiferromagneticCu(tn)Cl2

21 . . MagnetizationMeasurementsofα-UraniumUsingaPiezoresistiveCantileverinPulsedMagneticFields

23 . . anElectronicInstabilityinBismuthFarBeyondtheQuantumLimit

24 . . Electricalreadoutof31PspinQubitsinCrystallinesiliconathighMagneticFields

25 . . topologicalQuantumComputingwithread-rezayistates

26 . . nanodropletFormationinsolidsolutionsofVeryDilute3heinsolid4he

28 . . highresolutionMiniatureDilatometerBasedonaFMPiezocantilever

29 . . FirstaCheatCapacityMeasurementinCapacitor-Bank-DrivenPulsedFields

30 . . DecompositiontemperatureofMnBito45tesla

MaGnEtsCIEnCE&tEChnOLOGyEngineering materials, instrumentation, magnet technology, superconductivity-applied

32 . . CurrenttransportatGrainBoundariesinsuperconductingBa(Fe1-x

Cox)

2as

2Bicrystals

33 . . VortexLiquid-glasstransitionUpto60tinnano-engineeredCoatedConductors

35 . . .DevelopmentofhighCriticalCurrentDensityinMultifilamentaryround-wireBi2sr

2CaCu

2O

8+δby

strongOverdoping

36 . . In-situMeasurementsofMagneticallyDrivenMotionofspecificIndividualGrainBoundariesinZnwithahighFieldMagnetMicroscopyProbe

38 . . MrIEvaluationofadsorbedWaterinsolidsat21 .1t

39 . . DesignoftheMagnetLabsplitresistiveUserMagnetforscattering

3

ChEMIstryChemistry, magnetic resonance techniques, geochemistry

43 . . high-fieldQCPMGnMrofLargeQuadrupolarPatternsUsingresistiveMagnets

42 . . MrMicroimagingwithaCylindricalCeramicDielectricresonatorat21 .1t

44 . . EfficientDouble-resonanceCoilforLow-γMrIofLargerodentBrainsat21 .1tesla

45 . . InfluenceofPb(II)IonsontheEPrPropertiesofthesemiquinoneradicalsofhumicacidsandModelCompounds:highFieldEPrandrelativisticDFtstudies

47 . . high-FieldEPrandMagneticsusceptibilitystudiesontetranuclearFerromagneticQuinolineadductsofCopper(II)trifluoroacetate

48 . . ChemicalspeciationofCalciumandsodiumnaphthenateDepositsbyElectrosprayIonizationFt-ICrMassspectrometry

50 . . arobusttwo-Dimensionalseparationfortop-DowntandemMassspectrometryoftheLowMassProteome

LIFEsCIEnCEsBiochemistry and biology

52 . . solid-state35ClnMrspectroscopyofaVarietyofhydrochloridePharmaceuticals

53 . . ExploitingMarineCyanobacteriaforDrugDiscovery

55 . . KItKinaseMutantsshownovelMechanismsofDrugresistancetoImatinibandsunitinibinGastrointestinalstromaltumorPatients

56 . . In vivosodiumandProtonMrImagingofLargerodentsat21 .1t

58 . . anovelapproachtoDementia:highresolution1hMrIofthehumanhippocampusat21 .1t

59 . . MrMicroscopyofnerveFiberstructureattheCellularLevel;Validationoftractography

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on the cover:thecoverimagewaspulledfromafigure

showingangle-dependentquantum-oscillationdatainyBa

2Cu

3O

6 .56takeninthehybridmagnet .thework,

byP .a .Goddardet al.,hasbeenacceptedasanEditors’suggestioninPhysical Review Bandissummarizedonpage14 .

4 VolUMe 17 · no. 2

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N Welcometothe2009highlightsIssueFortheMagnetLab,2009wasayearofchangeandprogress–

changeinsomeofouroperationalproceduresandprogressinourownandourusers’research .thehighlightsof2009’sbreakthroughscienceareincludedinthisissueofMag Lab Reports,whichcanbefoundalongwithpastissuesatwww .magnet .fsu .edu/mediacenter/publications/ .theselectionsinthisissueshowcaseoutstandingresearchthatisrepresentativeofthequality,creativityandbreadthofthelab’sscientificuserprogram .theselectioncriteriaalsofavorresearchthatispublishedand/oradvancesanewtechniqueforuserresearchinhighmagneticfields .

aftercombingthrough416submittedresearchreportsfrom17categoriesrepresentingcondensedmatterphysics,magnetscienceandtechnology,chemistryandthelifesciences,thelab’sscienceCouncilmaderecommendationstotheDirector(that’sme),resultinginthe38highlightsincludedinthisissue .

äthisyear,submittedresearchreportsareupto416,roughlya10-percentincrease .

ä26percentoftheresearchactivities(82reports)werealreadypublishedin2009orareacceptedforpublicationthisyear,manyinprominentjournals .

äanadditional10percentweresubmittedforpublication;and35percenthavemanuscriptsinpreparation .

Whatpresentlyisthemostrapidlygrowingresearchtopicinhighmagneticfieldresearch?Inaword(andinasingleorbi-layer):Graphene .DuringthispastyearattheMagLab,grapheneresearchblossomedfromanexcitingnewfieldinvolvingjustafewusergroupstoamajorresearchprogramwith17differentvisitingusergroups .Weareparticularlypleasedthatsixofthe17groupsareheadedbynew principal investigatorsattheMagnetLab,atestimonytothevibrancy(andaccessibility!)ofhighmagneticfieldresearchinouruserprogram .(Checkoutpages8-14forarepresentativesamplingofrecentgrapheneresearch .)

anewprincipalinvestigatorisdefinedasanyscientistperforminghisorherfirstexperimentattheMagLabasaprincipalinvestigator .In2009,fullyone-thirdofthePIsinouruserprogramwere,thuslydefined,new .theMagnetLabreported118newPIs:28inthePulsedFieldProgram,23intheDCFieldProgram,21inIonCyclotronresonance(ICr),20inElectronMagneticresonance(EMr),15intheadvancedMagneticresonanceImagingandspectroscopyProgram(aMrIs),and11inthenuclearMagneticresonance(nMr) .

tocomplementthisgrowth,thelablaunchedastreamlinedUser portalforusersofanyoftheMagLabfacilitiestoapplyformagnettime(https://users .magnet .fsu .edu/) .theUserPortalisaccessibleinoneclickfromtheMagnetLabhomepage,andincludesalloftheMagnetLab’suserpoliciesandprocedures,aswellasthensFCooperativeagreementthatgovernsuseroperations .

InMarchof2009,theMagnetLab’slargestuserprogram,thedc Field program,rolledout“flextime”foritsusers .Magnetshiftswereextendedby2 .5hourseach,providingeachexperimentwith33percentmoremagnettime .Underflextime,eachuserisallocatedanenergybudgetandisfreetobestusethemegawatt-hoursforhisexperiment .DCmagnetusersalsowillwelcome–thoughtheyperhapswillnotevennotice–amulti-million-dollarreplacementoftheMagLab’scryogenicinfrastructure,begunin2009andcontinuingoverthenexttwoyears .Ifwewerenotabletoaddressthis“nuts-and-bolts”issue,thedecrepitsystemwouldhavereachedacrisisstatesoonerratherthanlater .

theMagLabdirector–speakingofdecrepit–turned50in2009 .

thepulsed Field Facilityinitiatedthefirstsetofuserexperimentsinthe85-teslamulti-shotmagnet .sixproposalswereselectedformagnettimewithfourbackupproposalsalsoselected .thisuniquemagnetsystemhasalreadyproducedpapersinPhysica B,Physical Review Letters andProceedings of the National Academy of Sciences .

theHigh B/t FacilityattheUniversityofFloridacommissionedafast-turnarounddilutionrefrigeratorannexadjacenttotheMicrokelvinLaboratory .this10-tesla,10-mKsystemallowsuserstotestsamplesanddebugnewlow-temperatureexperimentaltechniques .Onceeverythingisworking,theexperimentcanbetransferredtothehigh-fieldnuclear-demagnetizationcryostats,inwhichhighB/texperimentscantakeweeksorevenmonthstoperform .

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NtheeMR programwasenhancedinthesummerof2009withextendedfrequencycoverageto1thzandtheadditionofMössbauerspectroscopy .Inaddition,stevehill,directoroftheEMruserprogramsincehisarrivalatFsUin2008,commissionedthefruitsofhisFsUstart-uppackage:asecondEMrlabattheMagLab,featuringtwonewmulti-high-frequency(8-700Ghz)heterodyneinstrumentsforhigh-fieldEMrmeasurements .

ProbedevelopmentinournMR programcontinuedtosetthestandardin2009 .Magicanglespinning(Mas)triple-resonanceprobesweresuccessfullytestedtooperateat17,000revolutionspersecondononeofthe600-Mhzinstruments,layingthegroundworkfordevelopmentofanewsuiteofMasandalignedtriple-resonanceprobesat400,600,and900Mhzin2010 .

BycombiningnationalInstitutesofhealthandamericanrecoveryandreinvestmentact(“stimulus”)funds,aMRiscontractedin2009foranewconsoleandgradientsforthe11 .1-t/40-cmimagingmagnetandanewanimalMrIsystemat4 .7t/33cmwithanactivelyshieldedmagnet .thenewequipmentwillallowaMrIsuserstocapitalizeonstate-of-the-artdigitaltechnologyforpulsesequencegenerationanddataacquisition .theadditionofanimalimagingandspectroscopyspecialisthuadongZeng,whojoinedaMrIsinlate2009,willhelpusersgetthemostoutoftheupgradedsystems .

theicR user programcontinuedtoimprovetheresolutionformassspectroscopyofsmallmoleculesbyaddinganadditionalpumpingstagetoits14 .5-t,104-mmboresystem .ButthebiggestnewsbyfarforourICruserprogramwasthelateDecemberawardbythenationalscienceFoundationof$15milliontopurchaseastate-of-the-art,21-tsuperconductingmagnetsystem .Onwardtohigherresolution,highersensitivity,andhigherall-things-that-are-good .

Other2009facts:

äthe Magnet lab User collaboration Grants program,orUGCP,(viewablehere:www .magnet .fsu .edu/usershub/funding/index .html)supported41ofthe416researchactivitiesin2009 .theUCGPpromotesboldbutriskyresearchandtechniquedevelopmentattheMagLabbyencouragingcollaborationsamonginternalandexternalinvestigatorsandprovidinginitialseedmoneyfornewresearchprograms .UCGPgrantsareourprimary”bottomsup”mechanismforenhancingourmeasurementcapabilitiesandareresponsibleformanypublicationsinhigh-impactjournals,includingthreearticlesinNature,16inPhysical Review Letters,andsixintheJournal of the American Chemical Societyin2009 .

äthemajorityofuserresearchprojectsin2009werefundedbytheU .s .nationalscienceFoundation(justover50percent,includingtheMagLab’sUCGPgrants),theU .s .DepartmentofEnergy(approximately13percent),andtheU .s .nationalInstitutesofhealth(10percent) .Otherfundingorganizationsincluded:americanheartassociation,BurroughsWellcome,DanishnationalresearchFoundation,theDeutscheForschungsgemeinschaft(Germany),ElectricPowerresearchInstitute,agencenationaledelarecherche(France),IketaniscienceandtechnologyFoundation(Japan),JapansocietyforthePromotionofscience,KeckFoundation,KoreanationalresearchFoundation,nasa,nationalsciencesandEngineeringresearchCouncil(Canada),U .s .airForceOfficeofscientificresearch,U .s .army,U .s .navy,U .s .Departmentofagriculture,andnumerousuniversities .

asalways,ourprimarythanksgotoourusers,whoprovidethecompellingandvariedstuffthatfillseachannualhighlightsissue .Greatstuff .specialthankstoscienceCouncilChairalbertMiglioriandscienceCouncilmembersrafaelBrüschweiler,MarkEmmett,LevGor’kov,stephenhill,DavidLarbalestier,DenisMarkiewicz,DraganaPopovicandGlennWalter,thescientificbreadththatworkswithKathyhedick,theorganizationalbrawn,todrivetheselectionofthesehighlights .

rockandroll,

GrEGOrys .BOEBInGEr

6 VolUMe 17 · no. 2 special edition

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t EDUCatIOn,OUtrEaChanDDIVErsItyCutting-edgescienceistheMagnetLab’scoremission,butitwon’tbeeffectiveiffuturegenerationsdon't

understandandsupportit .theMagnetLabhasbecomeincreasinglycreativeinitsapproachtoreachingstudents,teachers,andthepublic,andinrecruitingpopulationstraditionallyunderrepresentedinthesciences .

susan Ray (Mag lab-FsU)

educationtheLab’sCenterforIntegratingresearch&Learning(CIrL)expandeditsnontraditionaloutreachwith

thelaunchof“Doingsciencetogether”in2009 .Doingsciencetogetheroffersbothkidsandadultsopportu-nitiestolearnabouttheirworldwithhands-onactivities .CIrLpartneredwithBarnes&noblebooksellersforaseriesofDoingsciencetogethernights,reaching750studentsandparents .

·“traditional”outreachwasprovidedto8,104K-12studentsin2009:7,155inclassroomvisitsand949whovisitedtheMagnetLabintallahasseefromsixcountiesinFloridaandGeorgia:Calhoun,Columbia,LeonandWakullacountiesinFlorida,andDecaturandthomascountiesinGeorgia .

·theresearchExperiencesforUndergraduatesprogramhosted21undergraduatestudentsfrom13differentcollegesanduniversitiesaroundtheUnitedstates .

·theresearchExperiencesforteachersprogramhosted13teachersfromsouthFloridatonorthernUtah .

·Partneringwithseveralotherorganizations,CIrLcontinueditsimmersivesummerprogrammingforgirls,calledsciGirls .

MagnetLabK-12EducationOutreachCoordinatorCarlosVillahostednearly950studentsattheMagLabin2009 .


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tdiversitytheMagnetLabaspirestobecomeanationallyrecognizedleaderinthediversityofitsscientific,

technical,andengineeringstaff,muchthesamewayitisalreadyrecognizedforitseducationandoutreach .Withthisgoalinmind,thelabin2009continueditsrecruitingpoliciesofincludingatleastonememberoftheMagnetLabDiversityCommitteeoneachsearchcommitteeforscientificandtechnicalstaff,andadvertisedjobopeningsinvenuesthattargetwomenandminorities .

Followingtherecommendationfromthe2008nsFsiteVisitreport,thelabexploredwaystoestablishtheDependentCaretravelGrantProgram,whichseekstoassistandadvancethecareersofunderrep-resentedgroupsincludingwomenbyprovidinggrantsfortravel-relatedexpensesfordependents .theDiversityCommitteedevelopedtheinitialproposal,andfurtherdiscussionsareunderwaywiththeFsUOfficeofresearch .alsoin2009,theFsUOfficeofDiversity&EqualOpportunityconductedatrainingprogramattheMagnetLab .

outreachOverthepastfewyears,thelabhasincreasinglylookedforwaystoengagethepublicbygivingthem

moreopportunitiestovisitthelab .OnJune17,2009,thelablaunchedstandingpublictoursthethirdWednesdayofeverymonthfrom11:30a .m .to12:30p .m .Morethan90peopleattendedthefirststandingtour .VisitorsarenotrequiredtocallaheadorrsVP;theyjustshowup .Previously,tourswereonlyavailableforpre-scheduledgroupsofeightorgreater .

Openhouse2009continuedthetrendofrecord-breakingattendancewith5,573visitors(seefigure1) .newfor2009wasapartnershipwithamerica’ssecondharvestFoodBankoftheBigBend .Openhouseguestswereaskedtobringacannedgoodorothernon-perishablefooditemastheunofficialpriceofadmission .Inall,theMagnetLabcollectedmorethan2,000poundsoffood .the2009OpenhousealsomarkedthedebutofthewildlypopularKidsZone,whichfeatureddemonstrationsandactivitiesforchildrenforpre-Kthrough5thgradeandopportunitiesforkidstoconnectwithlab’seducationalprogramming .

Mag lab open House 2009 by the numbers

number of visitors 5,573

PoundsoffoodcollectedforsecondharvestFoodBank 2,021

Cupsofcornstarchusedinoobleck(anon-newtonianfluid!) 1,440

numberofspectrumglassesgivenoutforvisitorstoseerainbows 1,000

numberofballoonsblownupinatmosphericpressuredemonstration 200

numberofPeepsblownupinatmosphericpressuredemonstration 150

Poundsofpotatoesfiredinpotatocannon 100

numberofparticipatoryscienceactivities 75

numberofcometscookedincomet-makingdemonstration 35

numberofquartersshrunkinshrinkingquartermachine 25

numberofCommunityClassroomConsortiumpartnersparticipating 14

Figure 1.


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S Understanding of the novel quantum hall effect in graphene, especially the behavior at the chargeneutral point where the density of states vanishes at zero field, remains an active area of research .Earlier transport studies in single layer graphene have shown that high magnetic fields lift the unusualfourfolddegeneracyofthezero-energyLandaulevel(LL)andleadtotheformationofagappedstate .Inbilayergraphene,ontheotherhand,thezero-energyLLhasaneightfolddegeneracy .thisreportdescribestransportmeasurementsonbilayergrapheneonasiO

2substrate,whichdemonstratethathighmagnetic

fieldscompletelyliftthedegeneracyandleadtotheinsulatingbehavioratthechargeneutralpoint,similartotheresultsonsinglelayergraphene .althoughthedatasuggestthatelectron-electroninteractionsmightberesponsiblefortheliftingofthedegeneracy,theoriginofthissymmetrybreakinginbilayergrapheneisstillunknownandmorestudiesaresuretofollow .

•thisworkwaspublishedinPhys. Rev. Lett.,104,066801(2010) .

symmetryBreakingoftheZeroEnergyLandauLevelinBilayerGrapheneY. Zhao (columbia University, physics); p. cadden-Zimansky (columbia University, physics & Magnet lab); Z. Jiang (Georgia institute of technology, physics); and p. Kim (columbia University, physics)

intRodUctionItshybridlinear-parabolicbandstructureandtheassociated2πBerryphaseofitschargecarriersmake

thephysicsofbilayergrapheneasdistinctfrommonolayergrapheneasthelatterisfromconventionaltwo-dimensionalelectronsystems .Inparticular,thesepropertiesleadtotheformationofanunprecedentedeightfolddegenerateLandaulevel(LL)thatformsatthechargeneutralcrossoverpointundersufficientlyhighmagneticfields .thisdegeneracyhaspreviouslybeendetectedbyobservingtheformationofsuccessivequantumhallplateausatν=-4andν=4fillingfactors .

expeRiMent ResUltsBysubjectinghighmobilitybilayergraphene(lowerinsetFigure1)tomagneticfieldsinexcessof25

tesla(t),thecompleteliftingofthiseightfolddegenerateLLcanbeobserved1 .asshowninFigure1,thehallconductanceatthelowestfielddisplaystheν=-4andν=4fillingfactorsthatmarktheinitialdegeneracy .asthefieldisincreased,newplateausemergeassuccessivesymmetriesarebroken,withplateauseventuallyappearingateachfillingfactor .

Figure 1 Figure 2

thesenewfillingfactorsalsocanbedetectedthroughthemeasurementofnewresistanceminimainthelongitudinalresistance .Byexaminingthebehavioroftheseminimaasthemagnitudeanddirectionoftheappliedfieldischanged,informationabouttheoriginofthesymmetrybreakingthatunderlieseachnewplateaucanbegained .Inparticular,thesensitivityoftheminimaatν=2&3totheperpendicularcomponentoftheappliedfieldratherthantothetotalfield(Figure2)indicatesthatthesestatesarenotformedbyconventionalZeemansplitting .


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SacKnowledGeMentsthisworkissupportedbytheDOE(no .DE-FG02-05Er46215) .

ReFeRences 1 .Zhao,y .,etal .,Phys. Rev. Lett .,104,066801(2010) .

Low-energyelectronicstructureofbilayergrapheneismadeoftwoFermipointswithquadraticdispersions .Usingrenormalizationgroup(rG)theorytostudylow-energyproperties,wefindthatthetwoquadraticFermipointsspontaneouslysplitintofourDiracpointsatzerotemperature .thisresultsinanematicstatethatspontaneouslybreaksthesixfoldlatticerotationsymmetryintoatwofoldone,withafinitetransitiontemperature .Criticalpropertiesofthetransitionandeffectsoftrigonalwarpingarealsodiscussed .

•thisworkwaspublishedinPhys. Rev. B Rapid Commun .,81(4),041401r(2010) .

Many-bodyInstabilityofCoulombInteractingBilayerGrapheneoskar Vafek, Kun Yang (FsU/Magnet lab)

intRodUctionLow-energyelectronicstructureof(unbiased)bilayergrapheneismadeoftwoFermipointswith

quadraticdispersions,iftrigonal-warpingandotherhighordercontributionsareignored .Weshowthatasaresultofthisqualitativedifferencefromsingle-layergraphene,short-range(orscreenedCoulomb)interactionsaremarginallyrelevant .WeuserGtostudytheireffectsonlow-energypropertiesofthesystem,andshowthatthetwoquadraticFermipointsspontaneouslysplitintofourDiracpointsatzerotemperature .thisresultsinanematicstatethatspontaneouslybreaksthesixfoldlatticerotationsymmetry(combinedwithlayerpermutation)downtoatwofoldone,withafinitetransitiontemperature .Criticalpropertiesofthetransitionandeffectsoftrigonalwarpingarealsodiscussed .

ResUlts and discUssionInthisworkweapplytherGmethodtothebilayergraphenewithBernalstacking .Whileingeneral,the

motionofthenon-interactingelectronsinsuchpotentialdoesnotleadtodivergingsusceptibilitiessincetheenergyspectrumhastwosetsoffourDiracpointsinthecornersoftheBrillouinzone(duetotrigonalwarping),ifonlynearestneighborhoppingisconsidered,eachsetoffourDiracpointsmergesintoasingledegeneratepointwithparabolicdispersion .asthenearestneighborhoppingamplitudesarethelargest,thelatteristhenaturalstartingpointoftheoreticalanalysis .


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S next,wedeveloptheeffectivetheoryforthelowenergydegreesoffreedom,findingthatifwestartwiththeinteractioninthedensity-densitychannelonly,twoadditionalcouplingconstantsaregenerated .WethereforetracktherGflowofthethreecouplingconstantstofindthattheyalldivergeataspecificenergyscale,whichweassociatewiththetransitiontemperature .Whileallthreecouplingsdiverge,theirratiosflowtonon-trivial(universal)numbersshowninthefigurebelow .

thesolutionoftherGflowequationsallowsustoanalyzetheflowofthesusceptibilitiestowardvariousbrokensymmetrystates .Wefindthesusceptibilitiesin15particle-holechannelsand16particle-particlechannelstofindthatthemostdivergentoneisthenematicchannel .

conclUsionsthisleadsustotheinterestingconclusionthatatlowenoughtemperature,theCoulombinteractions

leadtotheelectronicnematicstateviaacontinuousphasetransition .thisstatebreaksthethreefoldrotationalsymmetry,butdoesnotbreakthe(lattice)translationalsymmetry,makingitdistinctfromstripes .Moreover,whileinthecontinuumapproximationthetransitionwouldbeofKostrelitz-thoulesstype(infiniteorder)thepresenceofthethreefoldsymmetryallowsforathird-orderorderparameterinvariant .thisputsthetransitionintheuniversalityclassofthe3-statePottsmodel,i .e .thetransitionremainscontinuousdespitebeingfirstorderwithinthemean-fieldapproximation .

ReFeRences 1 .Vafek,O .andyang,K .,Phys. Rev. B Rapid Commun .,81(4),041401r(2010) .

theremarkablepropertiesofepitaxialgraphene(EG)grownonsiliconcarbidehavemadeitapromisingplatform for graphene-based electronics . an interesting question that remained to be addressed iswhethertheelectricalpropertiesofepitaxialgrapheneonsiCareessentiallythesameasthoseinexfoliatedgraphenefilms,wheretheobservationofthequantumhalleffect(QhE)waspivotalforgrapheneresearch .the group from Purdue examined gated, few-layer EG films grown on the si-face of 4h siC substrates .theyobservedwell-definedQhEthatreproducestheuniquefeaturesexhibitedbyexfoliatedsingle-layergraphene, including a Berry phase of π .the electrical properties of films were retained after gate stackformation without significant degradation . the user group from Georgia tech studied a high-mobilitysingle graphene layer grown on the C-face of the same substrate .the mobility was comparable to thebestexfoliatedgrapheneflakesandanorderofmagnitudelargerthansi-faceEGmonolayers .thegroupdemonstratedthecharacteristicQhEwithaBerryphaseofπ .theresearchershavealsoshownthatQhEisinsensitivetoprocessinginduceddisorder .theseimportantexperimentsbringepitaxialgrapheneyetastepclosertobecomingascalableplatformforgraphene-basedelectronics .

Pronouncedhalf-IntegerQuantumhallEffectonEpitaxialGrapheneupto70Ktian shen, adam t. neal, Jiangjiang Gu, Min xu, Yanqing wu, Mike Bolen, Michael a. capano, and peide d. Ye (purdue University, electrical and computer engineering); lloyd engel (Magnetlab)

intRodUctionrecentreportsoflarge-areaepitaxialgraphenebythermaldecompositionofsiCwafershaveprovided

themissingpathwaytoaviableelectronicstechnology .1-5aninterestingquestionthatremainstobeaddressediswhethertheelectricalpropertiesofepitaxialgrapheneonsiCareessentiallysameasthoseinexfoliatedgraphenefilms .5-7Forexample,thewell-knownquantumhalleffect(QhE),adistinguishingfeatureofatwo-dimensionalelectronicmaterialsystem,isjustbeginningtobediscoveredinepitaxialgraphene .8-10WereportontheobservationoftheQhEingatedepitaxialgraphenefilmsonsiC(0001),alongwithpronouncedshubnikov-dehaas(sdh)oscillationsinmagneto-transport .thelastQhplateauisespeciallypronounced,evenattemperaturesashighas70K,reachingthetemperaturelimitofthepresentexperimentalsetup .


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SResUlts and discUssion

Figure1showsthehallresistanceandmagneto-resistancemeasuredatt=0 .8Kwithfloatinggatebias .thehorizontaldashedlinescorrespondtoh/(4n+2)e2values .theQhEoftheelectrongasinepitaxialgrapheneshowsonequantizedplateauandtwodevelopingplateauinr

xy,withvanishing

rxx

inthecorrespondingmagneticfieldregime .Figure2showsthetemperaturedependenceofr

xxatVg=-5V .Pronouncedsdhminimumremain

upto70K .Figure3showsthetemperaturedependenceofr

xyatVg=-5V .apronouncedn=0

Qhplateauremainsupto70K .ExperimentswereperformedusingsCM-2attheMagnetLab’stallahassee,FL,headquarters .

Figure 2

Figure 3

Figure 1

conclUsionsInconclusion,ahigh-kgatestackonepitaxialgrapheneisrealizedbyinsertingafullyoxidized

nanometerthinaluminumfilmasaseedinglayerfollowedbyanatomic-layerdepositionprocess .theelectricalpropertiesofepitaxialgraphenefilmsaresustainedaftergatestackformationwithoutsignificantdegradation .atlowtemperatures,theQhEisobservedinepitaxialgrapheneonsiC(0001),alongwithpronouncedsdhoscillations .thisquantumexperimentconfirmsthatepitaxialgrapheneonsiC(0001)sharesthesamerelativisticphysicsastheexfoliatedgraphene .

acKnowledGeMentstheauthorswouldliketothankJ .a .CooperJr .andL .P .rokhinsonforvaluablediscussions,andG .

Jones,t .MurphyandE .PalmattheMagnetLabforexperimentalassistance .PartoftheworkongrapheneissupportedbynanoelectronicsresearchInitiativethroughMidwestInstituteofnanoelectronicsDiscovery,DarPaandIntelCorp .theMagnetLabissupportedbynsFGrantnos .DMr-0084173andECs-0348289,thestateofFlorida,andDOE .

ReFeRences 1 .y .Q .Wu,et al.,Appl. Phys. Lett.,92,092102(2008) . 2 .G .Gu,et al.,Appl. Phys. Lett ., 90,253507(2007) . 3 .J .s .Moon,et al.,IEEE EDL, 30,650(2009) . 4 .J .Kedzierski,et al.,IEEE TED,55,2078(2008) . 5 .C .Berger,et al.,Science,312,1191(2006) . 6 .K .s .novoselov,et al .,Science,306,666(2004) . 7 .y .Zhang,et al.,Nature,438,201(2005) . 8 .t .shen,et al.,Appl. Phys. Lett.,95,172105(2009) . 9 .J .Jobst,et al.,arXiv:0908 .1900v1 . 10 .X .Wu,et al.,arXiv:0908 .4112 .


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S halfIntegerQuantumhallEffectinhighMobilitysingleLayerEpitaxialGraphenexiasong wu (Georgia tech), Yike Hu (Georgia tech), claire Berger (cnRs & Georgia tech), walt de Heer (Georgia tech)

intRodUctiontheremarkablepropertiesofepitaxialgraphene(EG)grownonsiliconcarbide,likeitshighmobility

andgrapheneelectronicstructure1andthefactthatitcanbepatterned,havemadeitapromisingplatformforgraphene-basedelectronics2 .however,thequantumhalleffect(QhE)waselusive .theobservationoftheanomalousQhEinmicroscopicexfoliatedgrapheneflakesthatweredepositedonsiliconoxidesubstrates3waspivotalforgrapheneresearch .ItsabsenceinEGledtospeculationsaboutthequalityofEGandtheeffectofthesiliconcarbidesubstrateontransport .thedemonstrationoftheQhEinthepresentexperiment4inpatternedEGisanimportantmilestoneingraphenescience .

expeRiMentalanEGmonolayerwasgrownonasemi-insulatingsiliconcarbidesubstrate2andcharacterizedby

atomicforcemicroscopy,ellipsometryandramanspectroscopy .theEGlayerwaselectron-beampatternedtoproduceahallbarstructureandmetalcontactpadswereapplied .thesCM2facilityattheMagnetLabwasused .transport(longitudinalandtransverse–hall-resistance)measurementswereperformedupto18tesla(t)at4K .thechargedensitywascontrolledbyadjustingtheexposuretohumidityaswellasbyexposuretoambientlight .

ResUlts and discUssionFromthetransportdata,themobilityofthesampleis20,000cm2/V·s .thehigh-fieldexperimentshows

awellresolvedQhE(seeFigure):quantumhallplateausareobservedinthemagneticfielddependenceofthehallresistance .thehallplateauscorrespondtotransverseresistancesρ

xy=(h/4e2)/(n+1/2)forn=0to

3,wheren istheLandaulevelindex,whichestablishesthenontrivialBerry’sphaseofπ .thelongitudinalresistivityρ

xx showsthecharacteristicshubnikov-dehaasoscillations,inwhichLandaulevelsfromn=0upto

n=7areeasilyrecognized .theoscillationsdevelopintotheQhEinhighfields,manifestedbycharacteristiczeroresistanceminimaandhallplateaus .DespitethefactthatthegrapheneisdrapedoverseveralsiCsteps,isheavilycontaminatedandhaspleats(seeaFMimageinthefigureinset),themobilityishighandtheanomalousQhEisunambiguouslyobserved .

Figure 1.Quantumhalleffectinsinglelayerepitaxialgraphene .InsetaFMimageofthepatternedgraphenedrapingoverthesiCsteps .


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SconclUsionsthequantumhalleffect,withaBerry’sphaseofπisdemonstratedforthefirsttimeonasingle

graphenelayergrownontheC-faceof4hsiliconcarbide .themobility(20,000cm2/V·sat4K)iscomparabletothebestexfoliatedgrapheneflakesonsiO2andanorderofmagnitudelargerthansi-faceepitaxialgraphenemonolayers .WehavealsoshownthatQhEisinsensitivetoprocessinginduceddisorder .theseresultsandotherpropertiesindicatethatC-faceepitaxialgrapheneisanidealplatformforgraphene-basedelectronics .

acKnowledGeMentsthisworkwassupportedbynsFunderGrantno .DMr-0820382andtheW .M .KeckFoundation .We

thankZ .G .Jiangforinsightfuldiscussions,andacknowledgeE .C .Palm,t .P .Murphy,J .-h .Park,G .E .Jonesforexperimentalassistance .

ReFeRences 1 .Berger,C .,et al .,Science, 3012,1191(2006) . 2 .Berger,C .,et al .,J. Phys. Chem .B,108,19912(2004) . 3 .Zhang .y .B .,et al.,Nature,438,201(2005) .

4 .X .Wu,et al .,Applied Physics Letters, 95,223108(2009)

high magnetic fields lift the fourfold degeneracy of the zero-energy Landau level (LL) in single layergrapheneandleadtotheformationofagappedstate .theprecisemechanismhasbeenasubjectofintensetheoreticalstudy,withelectron-electroninteractionsexpectedtoplayacriticalrole .sincetransportmeasurements are not suitable for detailed studies of a gapped state, the authors of this report haveutilizedinfraredmagnetospectroscopytoinvestigatethezero-energyLLinmonolayergrapheneonasiO

2

substrate .this technique issensitive to thecyclotronorbitsofchargecarriers that formthroughout theentiregraphenesheet .Unexpectedandsizableshiftsinthecyclotronresonance(Cr)transitionenergiesareobservedasafunctionoftheLLfillingfactorandappliedfield .theshiftsareattributedtoelectron-electroninteractionsthatnucleateagapinthen=0LL,therebyaffectingtheenergiesofCrtransitionstoandfromthislevel .

•thisworkwaspublishedinPhys. Rev. Lett .,104 (6),067404(2010) .

CyclotronresonanceattheChargeneutralPointofGraphenee. a. Henriksen (columbia University, physics), p. cadden-Zimansky (columbia University, physics & Magnet lab), Z. Jiang (Georgia institute of technology, physics), Z. Q. li (columbia University), l.-c. tung (Magnet lab), M. e. schwartz (columbia University, physics), M. takita (Barnard college, physics), Y.-J. wang (Magnet lab), p. Kim (columbia University, physics), and H. l. stormer (columbia University, physics & applied physics & alcatel-lucent)

intRodUctionOneofthecentralproblemsofgrapheneisgaininganunderstandingofitselectronicbehaviorat

thechargeneutralpoint(CnP),wherethedensityofstatesvanishesatzerofield,auniqueparticle-holesymmetricLLformsatmoderatefields,andadivergentlongitudinalresistanceisobservedathighfields .thedivergentresistanceprecludesaconventionalcharacterizationoftheunique“n=0”LLusingstandardtransporttechniques,butthislevelisamenabletostudythroughCrtransitionsintoandoutofitthatareobservedbyinfrared(Ir)spectroscopy .

expeRiMental ResUltsByexaminingIrabsorptionofgrapheneathighfieldswhileitsFermilevelistunedthroughtheCnP,the

energyoftheCrtransitionsintoandoutofthen=0LLcanbeseendirectly .Whileasingle-electronpictureoftransitionsbetweendegenerateLLspredictsaconstantCrenergy,largeshiftsupward,ashighas20meV,areinvariablyseenintheresonanceenergyattheCnP1 .thefielddependenceoftheseshifts,andthelackofsuchshiftsintheinterbandCrtransitionsthatdonotinvolvethen=0LL,suggestthatahigh-fieldenergygapmayformattheCnP(Figure1) .asthenovellineardispersionrelationofthechargecarriersingraphenerendersKohn’stheorem(whichstatesthatCrisinsensitivetoelectron-electroninteractions)inapplicable,detailedmappingoftheseshifts(Figure2)hasthepotentialtorevealunderlyingmanybodyeffects .


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Figure 1 Figure 2

acKnowledGeMentsthisworkissupportedbytheDOE(DE-aIO2-04Er46133,DE-FG02-05Er46215andDE-FG02-07Er46451),

thensFunderDMr-03-52738,ChE-0117752,andDMr-0820382,Onr(n000150610138),nystar,theKeckFoundation,MicrosoftProject-Q,andthesrC-nrI-MInD .

ReFeRences 1 .henriksen,E .,et al .,Phys. Rev. Lett .,104 (6),067404(2010) .

two noteworthy reports come from one and the same group of the authors using the contactlessconductivitymethodforobservationofquantumoscillations(QO) .amongthefindingsare:theshapeoftheFermisurfaceasdeducedfromtheangulardependenceoftheQO-oscillationfrequency;theangularvariationoftheeffectivemass;andtheLIfshitz-Kosevitchformoftheoscillations .resultsfromP .Goddardet al.includetheobservationofcorrugationsoftheFermisurface(Fs)cylindercausedbytheperpendicular-to-planetunneling .additionalanalysisofdatabys .sebastianet al.showstheapplicabilityoftheLandauFermiliquidconcept .

WhatCanWeLearnfromtheangle-dependenceofQuantumOscillationsinyBa

2Cu

3O

6+x?

p. a. Goddard (University of oxford); suchitra sebastian (University of cambridge); n. Harrison (Magnet lab-lanl) M. M. altarawneh (Magnet lab-lanl); c. H. Mielke (Magnet lab-lanl); Ruixing liang (University of British columbia); d. a. Bonn (University of British columbia); w. n. Hardy (University of British columbia) and G. G. lonzarich (University of cambridge)

two-axisrotationinfixedmagneticfieldsisapowerfultoolforinvestigatingthetopologyoflow-dimensionalFermisurfaces .Inparticular,forhighlyanisotropicmaterials,measuringtheresistivitywhilerotatingthesampleinanappliedmagneticfieldisoftentheonlytechniquethatcandeliverinformationontheFermisurface(Fs)shapeandthenatureoftheinter-planetransportinthebulkofthematerial .

Inlow-dimensionalmetallicsystemstheFsisusuallymadeupofquasi-one-dimensional(Q1D)sheetsand/orquasi-two-dimensional(Q2D)cylinderswithaslightwarpingduetotheinterlayerelectronictransfer .Magneticquantumoscillations(QOs)aresensitivetoclosedquasiparticleorbitsontheQ2DFssectionsandcanbeusedtodeterminethecross-sectionalareaofthesepocketsperpendiculartotheappliedmagneticfield,aswellasprovidinginformationregardingtheeffectivemassesandscatteringrates1 .however,whenthewarpingoftheFsisverysmallitisdifficult,sometimesimpossible,toextractinformationregardingtheshapeofthepocketsfromanangle-dependenceoftheQOs .thisisbecausethechangeinfrequencyoftheQOsonrotationwillbedeterminedsolelybythecosineoftheanglebetweenthecylinderaxisandthemagneticfield,nomatterwhatshapethefootprintoftheQ2DFsmightbe .theserestrictionsarerelaxedwhenthewarpingoftheFsislargerinmagnitudethantheseparationbetweenLandaulevels .atthefieldsatwhichthisistrue,itshould,inprinciple,bepossiblenotonlytoresolveseparateQOsfortheso-calledneckandbellyorbits(originatingfromthenarrowestandwidestcross-sectionsoftheFs),butalso


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Stodeduceinformationregardingthein-planefootprintoftheFsfromthedeviationsoftheQOsfromthesimplecosineangular-dependence2,3 .Wehaveattemptedtolookforsignaturesofsuchwarpinginanumberofunconventionalsuperconductors .herewepresentpreliminarydataforyBa

2Cu

3O

6+xfortwocompositions:

x=0 .54and0 .56 .

thesampleswerepreparedattheUniversityofBritishColumbia .theQOsweredetectedusingthecontactlessconductivitymethod,whichissensitivetochangesinskindepthviachanges(Df)infrequencyofaresonantcircuit4 .thesestudiestakeplaceatlowtemperaturesinordertomaximizetheamplitudeoftheQOs .highfieldsarerequiredtoovercometherobustsuperconductivitydisplayedbythematerialsandallowtheQOstobeseen .Fixedfieldsarenecessaryforcontinuousangularrotation .Forthesereasonsthe45-teslahybridmagnetattheMagnetLabintallahasseeistheonlyplaceintheworldthatexperimentslikethesecanbeperformed .

thefigureshowsangle-dependentquantum-oscillationdatainyBa2Cu

3O

6 .56takeninthehybridmagnet

atafieldof45tandatemperatureof1 .5Kandafterabackgroundhasbeensubtracted .θistheanglebetweenthec-axisandthemagneticfield .фistheazimuthalangleofrotationandrunsin15°stepsfrom-54°to154°(bottomtotop) .acompleteangle-dependencewasundertaken .thegapsinthedataresultfromacorrectionforasamplemisalignmentof~7° .Becauseofthesizeoftheinterlayertransfer,theeffectwearelookingforinyBa

2Cu

3O

6+xissubtle,butapreliminaryanalysisoftheangle-dependentdatasuggest

thatatleastoneQ2DFssectionisdetectedthathasasmallbutmeasurablewarpingandafootprintthatdeviatesfromsimplecircularsymmetry .theseresultshavebeenacceptedforpublicationasanEditors’suggestioninPhysical Review B .

acKnowledGeMentsWeacknowledgethesupportoftheU .s .DepartmentofEnergy,thenationalscienceFoundation,the

stateofFlorida,theroyalsociety,trinityCollege(UniversityofCambridge),andtheUKEngineeringandPhysicalsciencesresearchCouncil .

ReFeRences 1 .shoenberg,D .,Magnetic oscillations in metals (CambridgeUniversityPress1984) . 2 .harrison,n .andMcDonaldr .D .,J. Phys.: Condens. Matt ., 21, 192201(2009) . 3 .Wosnitza,J .,Int. J. Mod. Phys. B,7,2707-2741(1993) . 4 .altarawneh,M .M .,et al., Rev. Sci. Instr ., 80,066104(2009) .


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S LandauLevelPhysicsinanUnderdopedhightemperaturesuperconductoryBa

2Cu

3O

6 .56suchitra e. sebastian, G. G. lonzarich (U. of cambridge), Moaz altarawneh, chuck Mielke, neil Harrison (Magnet lab-lanl), d. a. Bonn, Ruixing liang, w. n. Hardy (U. of British columbia)

intRodUctionForthetwodecadessincethediscoveryofhighT

ccuprate,physicistshavebeenperplexedastothe

mechanismofsuperconductivitythat’sunconventionalinitsoriginandinitssurprisinglyhighvalue .Itisbelievedthatthestrangepropertiesofthe“normal”stateoutofwhichsuperconductivityoriginatesmayholdthekeytothismystery .Indeed,experimentssuchasphotoemissionandtransporthaveprobedthehigh-energyandhigh-temperaturepropertiesofthequasiparticlesthatprecedeCooperpairinginhighT

c

cuprates,yieldingpeculiarpropertiesthatdonotcorrespondtothoseofaconventionalFermiliquid .

Forthefirsttime,quantum-oscillationmeasurementsinultra-highmagneticfieldshavebeenabletoprobethelowenergypropertiesofnormalquasiparticlesincupratesuperconductorsbysuppressingthesuperconductingdome .Weareabletoprobetheselow-energypropertiesandcomparethemwithconven-tionalLandauquasiparticlestounderstandwhetherinfacttheFermiliquidpicturecompletelybreaksdowninunderdopedcuprates .herewepresentresultsoflowtemperaturedependentquantum-oscillationamplitudemeasurementsinaportabledilutionfridgeinthe45tesla(t)hybridmagnet,andangular-dependentquantum-oscillationfrequencyandeffectivemassmeasurementsinordertocomparethesewithconventionalFermimetalbehavior .

expeRiMentalthequantum-oscillationamplitudewemeasuredowntotemperaturesof100mK(figureonright)at

45tisseentosaturateatthelowesttemperaturesasexpectedforstandardFermiliquidbehavior,inwhichtheLifshitz-Kosevichformisobeyed .remarkablywefindthatthisstronglycorrelatedsystemyBa

2Cu

3O

6 .56,

insteadofcontraveningFermiDiracstatistics,infactobeysthemexactlyasexpected .

thepredominantquantum-oscillationfrequencyandeffectivemassareshownasafunctionoftheangleofinclinationofthemagneticfieldtothecrystallinec-axis(θ)inthefigureontheleft .heretooweseethatexactlyasexpectedfortheextremalFermisurfaceorbitsinaconventionallayeredsystem,aCosinedependence(greenline)isfollowedbothbythefrequencyandeffectivemassofasingleorbit .

ResUlts and discUssionLow-temperaturemeasurementsinultra-highmagneticfieldsenabledattheMagnetLabhavebegun

tooverturnconventionalwisdomintheunderdopedcupratesthathasperhapsstalledprogressinthisfieldforalmosttwodecades .thesequantum-oscillationmeasurementsmayindeedpavethewaytotheultimatebreakthroughinunderstandingunconventionalsuperconductivityinthesematerials .

ReFeRences 1 .sebastian,s .E .,et al.,http://arxiv .org/abs/0912 .3022(2009) . 2 .sebastian,s .E .,et al.,Phys. Rev. Lett .,103,256405(2009) .


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Sthe report of s . riggs et al. features the first ever measurements of the specific heat of underdopedyBCO6 .55

inhighmagneticfieldsupto45tesla(t)andt~10Kthatshowedtheremarkablesquare-rootdependence of the magnetic specific heat, B1/2, on the magnetic field . G .Volovik predicted this specificbehaviorforasystemofvorticesinsuperconductorswithad-waveorderparameterin1993 .theauthorsclaim that the dependence survives abovet

c giving support to the idea of pre-formed pairs . Quantum

oscillationsforthespecificheatareseenforthefirsttimeinthepresenceofthisbackgroundandinterpretedqualitativelyintheframeworkoftheLifshitz-Kosevichtheory .

highFieldspecificheatofUltracleanyBCO6 .55

:CoexistingFermiLiquidandd-wavesuperconductingGapscott Riggs (FsU, Mag lab); oskar Vafek (FsU, Mag lab); Jon Kemper (FsU, Mag lab); Greg Boebinger (FsU, Mag lab); Jon Betts (lanl, Mag lab); albert Migliori (lanl, Mag lab); doug Bonn (UBc); walter Hardy (UBc); Ruixing liang (UBc)

intRodUctionthetruenatureofthemagnetic-field-inducedresistivenormalstateinhightemperaturesupercon-

ductivity(htc)remainsamystery .therearetwoprominentschoolsofthought .Oneisthattheapplicationofmagneticfielddestroysthed-wavesuperconductinggaptouncoveracompetingstatewithlowenergyFermionicdegreesoffreedom .theotheristhatanappliedmagneticfielddestroyslong-rangephasecoherencebutlocalsuperconductivitysurvives .Bymeasuringthespecificheat,abulkthermodynamicprobeonultra-cleanyBaCuO

6 .55wedeterminethefieldevolutionofthequasi-particledensityofstateswell

intothemagnetic-field-inducednormalstateandfindco-existenceofbothphases .athighfieldsthespecificheatasafunctionoftemperaturefollowstheconventionalformexpectedforaFermiLiquid;CT = gT + bT

3

Ontheotherhandthefieldevolutionoftheelectronicquasi-particledensityofstatesfollowsasqrt(h)behaviorthroughtheentiremagneticfieldrangemeasured,evidencingafullydevelopedd-wavegap .Fromtheverysmallvalueofthespecificheatinthezero-temperaturelimit,weconcludethattheFermiliquidphenomenaarisefromasinglepocketofcarriersthatcoexistswithd-wavesuperconductivityinthecopper-oxygenplanes .thed-wavesuperconductinggappersiststoatleast45tmagneticfields,whichistwicethemagneticfield,h

irr,atwhichtheresistivetransitionoccurs .

Figure 1.LefthandpanelplotsthespecificheatdividedbytemperatureasafunctionofK2for0t(yellowcircles)and45t(bluetriangles) .BothfieldvaluesfollowthenormalFermiliquidformandgivethesameslopevalueforthephonons,establishingbasafieldindependentquantity .therighthandpanelplotstheelectroniccontributiontothespecificheatofyBCO

6 .55asafunctionofmagneticfield .the

datashowquantumoscillations(red)consistentwithaFermiliquid(blueoscillationsareafittothedata) .thedataalsoshowasqrt(h)dependenceuptothehighestfieldsmeasured,establishingthepersistenceofafullydevelopedsuperconductingd-wavegapuptoourhighestfieldsmeasured .


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S In2009therewerenumerousstudiesoftheironpnictides,recentlydiscoveredmaterialswithratherhightc(upto50Kinsomematerials) .thereportofa .Coldeaet al.deservesrecognition:thenon-superconductingmaterialCaFe

2P

2hasthecrystallineparametersclosetotheonesoftheso-calledcollapsedtetragonal(Ct)

phase of CaFe2as

2 that sets in under high pressure .the dhva experiments revealed the strongly three-

dimensionalFermisurfaceinCaFe2P

2 .theoutcomeisthatnestingfeatures/congruencybetweenthetwo-

dimensionalelectronandholeFermisurfacesseemtoplaytheessentialroleinthemagnetic,structuralandsuperconductingpropertiesofmostofthehtcsironpnictides .

•thisworkwaspublishedinPhys. Rev. Lett .,103,026404(2009) .

topologicalChangeoftheFermisurfaceinternaryIronPnictideswithreducedc/aratio:adehaas–vanalphenstudyofCaFe

2P

2

amalia i. coldea, c. M. andrew, a. F. Bangura, a. carrington (Bristol University, UK); J. G. analytis, J.-H. chu, i. R. Fisher (stanford University); R. d. Mcdonald (Magnet lab-lanl)

thesuperconductivityinironpnictidescanbeinducedeitherbydoping,appliedpressureorisoelec-tronicsubstitution .theisoelectricsubstitutionofpnictogen(aswithP)doesnotchangethenumberofFe3d electronsbutactslikeapplyingchemicalpressure,whichisequivalenttoappliedhydrostaticpressure .thisisforexamplethecaseofCaFe

2P

2,whichisaveryclosestructuralanalogueofthecollapsedtetragonal

phase(Ct)phaseofCaFe2as

2,whichoccursonapplyingpressure1 .yildirimhasarguedthattheCtphase

ofCaFe2as

2occurswhen,byreducingtheFemoment,theFe-asbondingweakensandthe(interand

intraplanar)as-asbondinggetsstrongercausingthesignificantstrongreductioninthecaxis2 .similarly,innonmagneticphosphides,thereductioninthec axis(orthec/a ratio)resultsinanincreaseP-Phybrid-izationbetweenpnictogenionsalongthec direction(closetothesinglebonddistance) .ConsequentlytheinterlayerP-Pdistanceapproachesthemolecularbondlength,justastheas-asdistancedoesintheCtphase .thespacerbetweentheironlayers(srorBa)limitsthedegreeofthishybridizationbetweenlayersandsuchastatewithstrongpnictogenbondingisunlikelytooccur .thisstateofreducedc/a ratiohasadifferentFermisurfacetopologycomparedtoLaFePO[3]orsrFe

2P

2[4] .

WehaveexperimentallymeasuredtheFermisurfaceofCaFe2P

2usinglow-temperaturetorque

magnetometryupto45tesla(t) .WefindtheFermisurfaceofCaFe2P

2todifferfromotherrelatedternary

phosphidesinthatitstopologyishighlydispersiveinthec axis,beingthreedimensionalincharacterandcomposedofalargeholesheetintheformofaflatpillowatthetopofthezonewhereastheelectronsheetsarestronglydistortedquasi-twodimensionalcylinderscenteredonthezonecorners .themassenhancementisidenticalonbothelectronandholepockets(~1 .5)beingmainlydeterminedbyelectron-phononinteraction .Ourresultssuggestthatwhenthebondingbetweenpnictogenlayersbecomesimportantnestingconditionsarenotfulfilledandmayexplainwhythesuperconductivityisabsentinsuchastate .theseresultshavebeenpublishedinPhysical Review Letters5 .

Figure 1.a)QuantumoscillationsinCaFe

2P

2obtainedusingtorque

magnetometry .b)theangulardependenceofthefundamentalfrequencies(relatedtotheextremalareasoftheFermisurface) .theresultingFermisurfaceofCaFe

2P

2 .


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SacKnowledGeMentsthisworkwassupportedfinanciallybyEPsrC(U .K .)andtheroyalsociety .Workatstanfordwas

supportedbytheU .s .DOE,OfficeofBasicEnergysciencesundercontractDE-aC02-76sF00515 .WorkperformedattheMagnetLabintallahassee,Florida,wassupportedbynsFCooperativeagreementno .DMr-0654118,bythestateofFlorida,andbytheU .s .DOE .

ReFeRences 1 .torikachvili,M .s .,et al .,PRL,101,057006(2008) . 2 .yildirim,t .,PRL,102,037003(2009) . 3 .Coldea,a .I .,et al .,PRL,101,216402(2008) . 4 .analytis,J .G .,et al .,PRL,103,076401(2009) . 5 .Coldea,a .I .,et al .,PRL,103,026404(2009) .

togetherwithusersfromItaly,M .Puttiet al.reporthigh-fieldspecific-heatmeasurementsonthesmandCemembersoftherare-earth(rE)familyrEFeasO,theparentcompoundsofthenowfamousFe-basedoxypnictidehigh-t

csuperconductors .IncontrasttotheotherrEmembers(Ce,Pr,nd),thelow-temperature

antiferromagneticphaseassociatedwiththesmcompoundisextremelyrobustagainsttheapplicationoflargemagneticfields .thispropertyisattributedtotheuniaxialanisotropyofthesm3+ ion,whichisalsouniquetothisfamily .

•thisworkwaspublishedinPhys. Rev. B, 80,214404(2009) .

MagneticOrderingoftherElatticeinrEFeasO:theOddCaseofsm .aspecificheatInvestigationinhighMagneticFieldM. putti (University of Genova, italy); s. Riggs, c. tarantini, J. Jaroszynski, a. Gurevich (Magnet lab); a. palenzona, t. duc nguyen, M. affronte (University of Modena and Reggio emilia, italy)

intRodUctionasharppeakinthespecificheatdataofsmFeasOwasfoundat5 .4Krelatedtotheantiferromagnetic

(aFM)orderingofsm3+ .Preliminarymeasurementsshowedthatthispeakisratherindependentoftheappliedmagneticfield,differentlyfromthecasesofCeFeasOandPrFeasOthatexhibitsimilaraFMtransitionrelatedtotheorderingoftherareearth .Duetothefieldresilience,thestudyoftheaFMorderingofsm3+requiresahigh-fieldinvestigation .

ResUlts and discUssion

Figure 1.specificheatversustofsmFeasOupto35t .

Figure 2.specificheatversustofCeFeasOupto7t .

specific-heatmeasurementswereperformedinsmFeasOintemperaturerangearoundtheaFMtransitionupto16tesla(t)inaPPMssystemandfrom20tto35tattheMagnetLabandinCeFeasOin


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S aPPMssystemupto7t .Figure1showsasharppeakofsmFeasOattn=5 .4KcorrespondingwithaFMtransition .theanomalyremainsverysharpupto16tandbecomesroundedwithlittleshiftintemperatureathigherfields .theinitialslopeoftheorderingcriticalfielddB

c/dtis160t/KwithB

c(t)definedatthepeak

ofthespecificheatanomaly1 .theinsensitivitytotheapplicationofanexternalmagneticfieldisuniquetosmandisnotobservedinCeFeasOwhoseanomalyshiftswithinitialslopedB

c/dt=5 .7t/K(seeFigure2) .We

arguethatsmFeasOpresentsanunprecedentedcaseofspinreorientationattheaFMtransition .recentneutrondiffractionscatteringmeasurements2showthatsm3+hasuni-axialorderparalleltothec-axis,withFMorderingintheab-planes,orderedaFMalongthec-axis,whichisalsouniqueinthefamilyofrEFeasOoxypnictideswhereCe3+,Pr3+andnd3+orderaFMwiththespinsalongtheab-planes .

conclUsionsWehaveperformedspecific-heatmeasurementsonsmFeasOsampleupto35tinordertoinvestigate

themagnetictransitioninvolvingthesmsublattice .thespecific-heatanomalyinsmFeasOrevealsasurprisinginsensitivitytotheapplicationofstrongmagneticfields .ComparingourresultstoCeFeasOwearguethatthepeculiarityofthesmFeasOisrelatedtotheuniaxialmagneticanisotropy .

acKnowledGeMentsthisworkwassupportedbynsFCooperativeagreementno .DMr-0654118,thestateofFlorida,the

DOEandtheItalianForeignaffairsMinistry(MaE) .

ReFeRences 1 .riggs,s .,et al .,Phys. Rev. B,80214404(2009) . 2 .ryan,D .h .,et al .,Phys. Rev. Binprint .

Usersfromslovakiareportmagneticsusceptibilitymeasurementsontheantiferromagneticcompound,Cu(tn)Cl2,atthehighB/TfacilityinGainesville .thismaterialhadbeenidentifiedasapotentialmodel

systemforstudyingeffectsofspin frustrationona two-dimensional (2D) triangular lattice, i .e . thespinscannotsatisfyallnear-neighborinteractionssimultaneouslyinthisgeometry .however,amagneticphasetransformation is observed, which is reminiscent of the so-called Berezinskii-Kosterlitz-thouless (BKt)transitionexpectedforatruly2Dantiferromagnet .

•thisworkwaspublishedinPhys. Rev. B,80,144418(2009) .

InterplayofFrustrationandMagneticFieldforthe2DQuantumantiferromagneticCu(tn)Cl

2a. orendáčová, e. Čižmár, l. sedláková, J. Hanko, M. Kajňaková, M. orendáč, V. Zeleňák, a. Feher (p. J. Šafárik University, Košice, slovakia); J. s. xia, l. Yin, d. M. pajerowski, M. w. Meisel (UF physics and Magnet lab); s. Zvyagin, J. wosnitza (Hochfeld-Magnetlabor dresden, Germany)

intRodUctionIn2006,the2DquantumantiferromagnetCu(tn)Cl

2(tn=1,3-diaminopropane=C

3h

10n

2)wasidentified

asapotentialmodelsystemfortherealizationofthespatiallyanisotropictriangularlatticefromthecollinearnéelphase1 .Inzerofield(B=0),noevidenceforlong-rangemagneticorderwasobserveddownto60mK,andthedatasuggestednearest-neighbor(J/k

B=3K),frustratingnext-nearest-neighbor(0<J’/J<0 .6),and

interlayer(|J’’/J|=10-3)interactions .themotivationofthepresentwork2wastoexploretheresponseofCu(tn)Cl

2inB>0,especiallyatT


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S(B<1t)isdominatedbyabackgroundeffect .the“shoulder”signatureobservedabove6tisassociatedwiththesaturationmagneticfieldBsat

(t→ 0)=6 .6t .thesedataresolvedacrucialboundaryofthemagneticphasediagram2 .

Figure 1.MagneticfielddependenceoftheisothermalacsusceptibilityofCu(tn)Cl

2 .Inset:

Magneticfielddependenceofthenormalizedmagnetizationat40mK .

conclUsionstheanalysisofallofthedataallowstheconstructionofthemagneticphasediagram2,whichis

remarkablyconsistentwiththeonepredictedforaBKtphaseonasquarelatticewithoutafrustratinginteraction3,exceptthatB

satisshiftedtovalueslowerthanexpected .

acKnowledGeMentsElementsofthisresearchwereperformedintheMagnetLabhighB/tFacility .thisworkwassupported,

inpart,byVEGaunderGrantno .1/0078/09,Projectno .aPVV-0006-07,EsFrnPprogram“highlyFrustratedMagnetism,”nsFunderGrantno .DMr-0701400,theMagnetLabviacooperativeagreementnsFunderGrantno .DMr-0654118andthestateofFlorida,DeutschePhysikalischeGesellschaft(DPG),andEuroMagnEtII .MaterialsupportfromU .s .steelKošices .r .o .isgreatlyacknowledged .

ReFeRences 1 .Zeleňák,V .,et al.,Inorg. Chem.,45,1774-1782(2006) . 2 .Orendáčová,a .,et al.,Phys. Rev. B,80,144418(2009) . 3 .Cuccoli,a .,et al.,Phys. Rev. B,68,060402(r)(2003) .

Uraniumgoesthroughaseriesoflatticechangeswhilecooling(t~43,37and23K),resultinginachargedensitywave(CDW)stateatlowtemperatures .IthadbeenpreviouslyassumedthattoobservequantumoscillationstheCDWstatemustbesuppressedbyappliedpressure .reportedhereareobservationsofdehaasvanalphen(dhva)oscillationsinα-uraniumatambientpressure, indicatingadensityofelectronicstatesattheFermienergy,inconflictwithasimpleCDWpicture .

•thisworkwaspublishedinPhysical Review B,80,241101(r)(2009) .

MagnetizationMeasurementsofa-UraniumUsingaPiezoresistiveCantileverinPulsedMagneticFieldsd. Graf, R. stillwell, R. d. Mcdonald, c. M. Mielke, F. F. Bakariev, s. w. tozer (Magnet lab)

intRodUctionthealphaphaseofuranium(a-U)providesauniquesettingtounderstandtheroleoff-electronsinthe

actinides .a-Uundergoesthreelow-temperaturechargedensitywave(CDW)transitionsattemperaturesof43,37,and23K,resultinginthevolumeoftheunitcellbelow23Kgrowingbyafactorof72to6000Å3 .ObservingtheFermisurfaceofthiselementwithoutfirstsuppressingthecomplexstructurecreatedbythe


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S CDWtransitionwaspreviouslyconsideredunlikely .highqualitysinglecrystalshavebeenrefinedthroughannealingtoproduceunprecedentedresidualresistivityratiosashighas570 .Improvedmagnetictorquemeasurementtechniquesinpulsedfields1haveallowedtheobservationofquantumoscillationsina-U2 .

expeRiMentalthemagnetizationofa-Uwasmeasuredwithasampleattachedwithsilicongreasetothe

measurementarmofapiezoresistivecantilever .thecantileverwasmountedonarotationprobeandcenteredina65tesla(t)short-pulsemagnet .CantileverresistancechangescreatedbytorquefromthesampleweremonitoredbyincorporatingthecantileverintoaWheatstonebridge .themeasurementtemperaturesarefarbelowthelowestCDWtransitionat23K,sothelatticedistortionsleavethesampleinthecomplex“a

3”state .

ResUlts and discUssionInfigure1,magnetizationmeasurementsfromfieldpulsesupto65tareshown .Onlythedatafrom

themagneticfielddownsweepsareshownandoffsetforclarity .ClearquantumoscillationsareobserveduptothemaximumfieldandthefastFouriertransformsareshowninthefigureinset .themeasuredorbitfrequency(F~570t)agreeswellwithDCfieldmeasurementswiththeappliedmagneticfieldalignedbetweentheaandc-axes .

Figure 1.PrCmeasurementsofthedhvaeffectfora-uranium .Inset:FastFouriertransformoftheshownmagnetizationresults .

conclUsionsMeasuringtheFermisurface(Fs)ofa-Uatambientpressureisasignificantstepforwardbutleads

tothequestion,howdotheCDWsaffecttheFstopology?schirberandarkomeasuredtheFsofa-Uunderpressuresabove8kbaralmost30yearsago3,allowingforcomparisonbetweenhigherandambientpressureresults .sofar,littleagreementhasbeenfoundbetweentheorbitsfoundunderpressure(ref .3,F~1300–2400t)andinthepresentmeasurements(80–1500t) .Inadditiontopressure,highmagneticfieldscanbeusedtosuppressCDWstatesbutsofar,wehavenotobservedanysignatureinmagnetizationmeasurementsthatsuggestaphasetransitionfromtheCDWstate .

acKnowledGeMentsthisworkwassupportbynsFCooperativeagreementDMr-0084713(MagnetLab)andDOE

DE-FG52-06na26193(sWtgroup) .

ReFeRences 1 .Ohmichi,E .,et al .,Rev. Sci. Instr .,73,3022(2002) . 2 .Graf,D .,et al .,Physical Review B,80,241101(r)(2009) . 3 .schirber,J .E .,et al .,Physical Review B,21,2175(1980) .


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SFortrigonal-axismagneticfieldsinbismuth,thelastLandaulevelisexpectedatB=9tesla(t) .however,recent experimental studies uncover a number of enigmatic effects beyond this quantum limit . Fornernstmeasurementsinbismuthupto45t,wefindevidenceforunidentifiedelectronicinstabilitiesbeyondthescopeofasimpleband-structuremodel .tounderstandtheseeffects,theorymustincludeelectronicinteractions,todateneglected,andtobecomesignificantabovethequantumlimit .

•thisworkwaspublishedintheNew Journal of Physics,11,113012(2009) .

anElectronicInstabilityinBismuthFarBeyondtheQuantumLimitBenoît Fauqué and Kamran Behnia (espci, paris, France)

intRodUctionWhenthefieldisappliedalongthetrigonalaxisofabismuthcrystal,nomorecrossingofthechemical

potentialbyanyknownLandaulevelisexpectedforB>9t .however,recentexperimentalstudiesofvariousphysicalpropertiesofbismuthuncoveranumberofenigmaticfieldscalesbeyondthisquantumlimit1-3 .Wehaveextendedthefieldrangeofthenernstmeasurementsinbismuthupto45tanduncoveredanewfieldscalepointingtoanunidentifiedelectronicinstability4 .

expeRiMentalnernsteffectwasmeasuredbyaminiatureone-heater-two-thermometerset-upspeciallydesignedto

workinthe45-thybridmagnet .thenernstdatawerecomplementedwithresistivitymeasurementsupto55tinapulsedfieldperformedintoulouse .

ResUlts and discUssionFigure1presentsthetransversevoltagegeneratedbyaconstantthermalgradientatt=1 .2Kasa

functionofmagneticfield .themainnewfindingisthedetectionofanernstpeakatB=37t,almostasdrasticasthechangecausedbythecrossingofthequantumlimitat9tandmuchlargerthanpreviouslydetected1ultraquantumnernstanomalies .

Figure 1.a. nernstsignalasafunctionofthemagneticfield .thenewpeakat38t(redarrow)ismuchlargerthanpreviouslyresolvedpeaks(blackarrows);b, c:samedataasafunctionofB-1 .Quantumoscillationsarevisiblebelowthequantumlimit(QL)markedbyablueverticalline .thefieldscalesbeyondthislimitarecausedbyunidentifiedmany-particleeffects .


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S conclUsionsOurfindingconstitutesthemostsolidexperimentalevidenceforafield-inducedelectronicinstability

beyondthescopeofthebandpicture .theexplanationofthisfieldscaleimpliesanappropriatetreatmentoftheelectronicinteractions,whichareneglectedinthispictureandareexpectedtobecomesignificantasthequantumlimitiscrossed .

ReFeRences 1 .K .Behnia,L .Balicasandy .Kopelevich,Science,317,1729(2007) . 2 .L .Li,et al.,Science,321,547(2008) . 3 .B .Fauqué,et al., Phys. Rev. B,79,245124(2009) . 4 .B .Fauqué,et al .,New J. Phys .,11,113012(2009) .

By combining pulsed electrically detected magnetic resonance (EDMr) and electron nuclear doubleresonance, researchers have realized a significant breakthrough in electrical readout of coherentlycontrollednuclearspins .Forthefirsttime,EDMrexperimentswereperformedathighmagneticfieldswithdevicespatternedbyelectronbeamlithographytohavenanoscalecontacts:just50nm×50nm

Electricalreadoutof31PspinQubitsinCrystallinesiliconathighMagneticFieldsc. Boehme, d. R. Mccamey (University of Utah, physics); G. w. Morley, p. studer, n. J. curson (University college london and london centre for nanotechnology); G. a. c. Jones, d. anderson (University of cambridge, physics); J. van tol (Magnet lab)

intRodUctionPhosphorus(31P)dopedsilicon(si:P)isatechnologicallyimportantmaterialwithpossibleusesin

spintronicandquantuminformationprocessingdevices .thegoaloftheworkdescribedinthefollowingwastocarryoutpulsedEDMrexperimentsathighmagneticfieldsinorderto(i)understandthesensitivitylimitationsofelectricalspinmeasurementson31Pand(ii)demonstrateelectricallydetectednuclearmagneticresonancebycombinationofpulsedEDMrandelectronnucleardoubleresonance .

iMpRoVinG tHe sensitiVitY oF pUlsed edMREDMrwasmeasuredinsi:Pdeviceswithcontactspatternedwithelectronbeamlithographytohave

activeareasof50nm×50nm .thesemeasurementsgenerallyreproducedthefeaturesdescribedinourpreviousresearchondeviceswithlargeractiveareas1-3,andusedthesamespectrometer4,5 .

Figure 1.Continuous-waveEDMratatemperatureof3Kwithabiascurrentof1 .6na .twoGaussianswereusedtofitthedata .

Figure 2.Conventionallydetected(black)andelectricallydetected(red)pulsedEnDOrof31Pdonorsinsi .theinsetshowsthepulsesequenceusedtomeasuretheelectricalsignal .thetoprowistheGhzradiationresonantwiththe31PelectronandthebottomtherFradiationwhosefrequencywassweptthroughthe31Pnuclearresonance .


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SFigure1showsaspectrumrecordedwithadevicehavingathicknessof500mmandaphosphorusconcentrationof1-3×1015cm-3 .thetworesonancesareduetothetwopossiblestatesofthephosphorusnuclearspin .theobservationthatoneislargerthantheotherreproducesourpreviousfindingthattheapplicationofwhitelightpolarizesthesenuclearspinsinamagneticfieldof8 .5tandatemperatureoflessthan3K .high-fieldEDMrhasnotpreviouslybeendemonstratedwithcontactssmallerthan10micrometerssoitisimportanttoquantifytheeffectofscalingthecontactsizesdown .Previousscalingstudiesoflow-fieldEDMrexperimentswithsi:Pfoundthatthesignal-to-noisewasapproximatelyindependentofthedevicesize6 .toscaledownfurtherwewilluseasilicon-on-insulator(sOI)waferwithadevicethicknessof100-300nm .

electRical nUcleaR spin detectionWehavealsodemonstratedpulsed,electricallydetectedelectronnucleardoubleresonance

(pEDEnDOr)onsi:P .Figure2showsbothaconventionallydetectedandelectricallydetectedsignalobtainedfromapulsedEnDOrexperiment .aresonanceisseenat~206 .7Mhzinbothcases .pEDEnDOrofthe29sinuclearspinsinthenaturallyabundantsiliconhostalsowereobserved .neithersignalhastheexpectedGaussianlineshape .thisisduetotheextremelylongnuclearspinlifetimes(>minutes)ofthe31Pdonors,whichleadtopassageeffectsevenatveryslowsweeprates .Ourproof-of-principledemonstrationofelectricalreadoutofcoherentlycontrollednuclearspinsathighfieldsprovidesapathwaytowardstheelectricalreadoutofnuclearspinqubits .thistechniquealsowillbeofwideruseasatoolforinvestigatingnuclearspinsinmacroscopicelectricaldevices,whichareusuallytoosmalltobeinvestigatedwithconven-tionalresonancetechniques .

acKnowledGeMentsWeacknowledgesupportfromtheMagnetLabVisitingscientistProgram .

ReFeRences 1 .McCamey,D .r .,et al.,Phys. Rev. B,78,045303(2008) . 2 .Morley,G .W .,et al .,Phys. Rev. Lett .,101,207602(2008) . 3 .McCamey,D .r .,et al .,Phys. Rev. Lett .,102,027601(2009) . 4 .vantol,J .,et al.,Rev. Sci. Instrum .,76,074101(2005) . 5 .Morley,G .W .,et al .,Rev. Sci. Instrum .,79,064703(2008) . 6 .McCamey,D .r .,et al.,Appl. Phys. Lett.,89,182115(2006) .

theread-rezayistates–asequenceoftwo-dimensional(2D)topologicallyorderedstates–maydescribeexperimentallyobservedfractionalquantumhalleffectsandmayalsopotentiallyberealizedinrotatingBosegases .theseareamongtheprimecandidatesforrealizingnon-abeliananyons,which, inprinciple,can be used for topological quantum computation . the present work generalizes our earlier work byfindingbraidingpatternsfortopologicalquantumcomputationandbyshowingpreciselyhowonewouldconstruct quantum gates to make realistic estimates of the resources required to carry out topologicalquantumcomputationusingtheseexoticstatesofmatter .

•thisworkwaspublishedinPhys. Rev. Lett.,103,160501(2009) .

topologicalQuantumComputingwithread-rezayistatesl. Hormozi (nist), s.H. simon (oxford), n.e. Bonesteel (FsU, physics)

intRodUctiontheread-rezayistatesaresequenceof2Dtopologicallyorderedstateslabeledbyintegerindexk

thatmaydescribetheexperimentallyobservedn =5/2(k=2)andn =12/5(k=3)fractionalquantumhalleffects .read-rezayistatesmayalsopotentiallyberealizedinrotatingBosegasesandareamongtheprimecandidatesforrealizingnon-abeliananyons,which,inprinciple,canbeusedfortopologicalquantumcomputation .Inthisworkwehavefoundaprescriptionforefficientlyfindingbraidsthatcanbeusedtocarryoutauniversalsetofquantumgatesonencodedqubitsbasedonanyonsoftheread-rezayistateswithk=3,k>4 .thisworkextendspreviousresults1,2,whichonlyappliedtothecasek=3(theso-calledFibonaccianyons)andclarifieswhy,inthatcase,gateconstructionsaresimplerthanforageneric

read-rezayistate .


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S ResUlts and discUssionalthoughthereareformalmathematicalproofsthatuniversalquantumcomputationispossibleusing

theread-rezayistateswithk>4,ourrecentwork3isthefirsttoshowpreciselyhowonewouldtranslateagivenquantumalgorithmintoabraidingpatternusingthem .Figure1showsoneofthebraidingpatternswehavefoundthatindicateshowacontrolled-Phasegatebetweentwoqubitsencodedusingfouranyonseachwouldbecarriedoutforthek=5read-rezayistate3 .

Figure 1.Braidingpatterntakenfrom[3]thatcanbeusedtorealizeacontrolled-Phasegatefornon-abeliananyonsdescribedbysU(2)

5Chern-simonstheory(theappropriatemathematicaldescriptionofanyonsinthek=5read-rezayistate) .Qubitsareencodedusingquadrupletsofanyonsandtimeflowsfromlefttoright .(Fordetailsofthenotationused,see[3]) .

conclUsionsthepresentworkgeneralizesourearlierworkonfindingbraidingpatternsfortopologicalquantum

computation,whichonlyappliedtoasingletypeofanyon(k=3),toaninfiniteclassofanyons(allintegerk>4) .Byshowingpreciselyhowonewouldcarryoutquantumgatesbybraidingtheseanyonsitbecomespossibletomakerealisticestimatesofthe(demanding)resourcesthatwillberequiredtocarryouttopologicalquantumcomputationusingtheseexoticstatesofmatter .

acKnowledGeMentsWorksupportedbyUsDOEGrantno .DE-FG02-97Er45639 .

ReFeRences 1 .Bonesteel,n .E .,et al.,Phys. Rev. Lett .,95,140503(2005) . 2 .hormozi,L .,et al.,Phys. Rev. B,75,165310(2007) . 3 .hormozi,L .;Bonesteel,n .E .;simon,s .h .,Phys. Rev. Lett.,103,160501(2009) .

UsersatthehighB/tfacilityperformednuclearmagneticresonance(nMr)studiestoprobethelocaldynamicsofverydilute 3he impurities insolid 4he,withthegoalof testing forchanges in the localmotionsnearthetemperaturesforwhichnon-classicalrotationalinertiafractionsmaypointtomacroscopicsupersolidflow .Previousexperimentsconfirmedthatthe3heimpuritiesdiffusebyquantummechanicaltunneling .thisworkisdesignedtotestwhether3heatomsbecomelocalizedatdislocationsorotherdefectsitesinthe“supersolid”region .thefindingsshowthatnanodroplets,ratherthanasolutionofliquid3he,areformedattheselowconcentrations .

nanodropletFormationinsolidsolutionsofVeryDilute3heinsolid4hes. s. Kim (UF, physics), c. Huan (UF, physics), l. Yin (UF, physics), J. s. xia (UF, physics), n. s. sullivan (UF, physics); d. candela (physics, Univ. of Mass.)

intRodUctionnMrstudieshavebeencarriedouttoprobethelocaldynamicsofverydilute3heimpuritiesinsolid

4he .thegoaloftheexperimenthasbeentotestforchangesinthelocalmotionsnearthetemperaturesforwhichnon-classicalrotationalinertiafractionshavebeenobserved1 .Itisthoughtthatthesefractionspointtomacroscopicsupersolidflow .additionof3heimpuritieshasbeenshownbyothers2tosuppresstheso-called“supersolid”effectsandourpreviousexperiments3haveconfirmedthatthe3heimpurities(atleastforconcentrationsdownto250ppm)diffusebyquantummechanicaltunneling4 .thenMrexperimentsaredesignedtoobservethemotionsdowntoapproximately10ppmandtotestwhether3heatomsbecomelocalizedatdislocationsorotherdefectsitesinthe“supersolid”region .


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SexpeRiMentaltwochallengeshadtobeovercometocarryouttheexperiments .First,becauseoftheweakthermal

relaxationprocessesforthenuclearspins,weneededtocarryouttheexperimentsatlowLarmorfrequenciesinordertokeeptheestimatedrelaxationratesbelowtheorderof104s .atlowtemperatures .second,becauseofthelowconcentrationandlowmagnetizationduetotherequiredlowLarmorfrequency,wedevelopedaspeciallowtemperaturepreamplifierthatcouldbeplacedadjacenttothenMrcoiltosignificantlyimprovethenMrsignaltonoise5 .Furthermoreanultra-quietradiofrequency(rF)environmentwasneedednecessitatingtheuseofthehighB/tFacility,whichisspeciallyequippedforrFshielding .

ResUlts and discUssiontheamplitudesofthenMrsignal(asmeasuredbytheamplitudeofasolidecho)areshowninFigure1 .

above120mKatypicalCurielaw(t-1)dependenceisobservedasexpectedfortheparamagneticbehaviorofthenuclearspins .Below120mK(atatemperaturethatvarieswith3heconcentration)oneobservesasharpchangewithaflattemperatureindependentbehavioratlowtemperatures .thistemperatureindependenceisunderstoodintermsoftheformationofnanodropletsofliquid3he .hysteresisisobservedoncyclingthroughthephaseseparationtemperature .

Figure 1.3heinsolid4he .temperaturedependenceofnMrechoamplitudeshowingphaseseparationandformationof3henanoclustersbelow150mK .

conclUsionsCarefulnMrstudiesof3heimpuritiesinsolid4hehaveshowntheformationofdropletsofliquid3hein

solid4heforverydilutesolutionsof3heinsolid4he .

acKnowledGeMentstheresearchwassupportedbytheMagnetLabthroughtheawardfromtheUserCollaborationGrants

Program .

ReFeRences 1 .Kim,E .,et al .,Nature,427,225(2004) . 2 .Kim,E .,et al .,Phys. Rev. Lett .,100,065301(2008) . 3 .Kim,s .s .,et al .,J. Low Temp. Phys .,158,584-589(2010) . 4 .richard,M .G .,et al .,J. Low Temp. Phys .,47,289(1982) .


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S thermal expansion is a fundamental thermodynamic quantity . Its accurate measurement in confinedspaces coupled with low temperatures and rapidly changing high magnetic fields suggests a newsensitivemillimeter-scaledilatometerthathaslittleornotemperatureandfielddependence .theauthorsdesignedanultracompactdilatometerusinganatomicforcemicroscope(aFM)piezoresistivecantilever(PrC)asthesensingelementanddemonstrateditsversatilitybystudyingthechargedensitywaves(CDWs)inalphauraniumtohighmagneticfieldsupto31tesla(t) .

•thisworkwaspublishedinRev. Sci. Instrum .,80,116101,2009 .

highresolutionMiniatureDilatometerBasedonaFMPiezocantileverJ.-H. park, d. Graf, t.p. Murphy, s.w. tozer (Magnet lab); G.M. schmiedeshoff (occidental college, physics)

intRodUctionthermalexpansion,ordilationofamaterial,iscloselyrelatedtothespecificheat,andprovidesuseful

informationregardingmaterialproperties .theaccuratemeasurementofdilationinconfinedspacescoupledwithotherlimitingenvironmentssuchaslowtemperaturesandrapidlychanginghighmagneticfieldsrequiresanewsensitivemillimeterscaledilatometerthathaslittleornotemperatureandfielddependence .WehavedesignedanultracompactdilatometerusinganaFMPrCasthesensingelementanddemonstrateditsversatilitybystudyingthechargedensitywaves(CDWs)inalphauraniumtohighmagneticfieldsupto31t1 .

desiGn and opeRationtheprincipleofoperationistomeasurethechangeinresistanceofanaFMPrCwhenthesample

dimensionschange .asschematicallyshowninFigure1(leftpanel),foraz-directiondilationmeasurement,thesampleandPrCaregluedtoasubstrate .thetipofthePrCgentlyrestsonthesamplewiththeaFMtipfacingupsuchthata1%changeinnominalresistanceisgeneratedtherebyassuringthatthetipandsamplewillnotseparateasthesamplecontractsuponcooling .theresistancesofthepiezoelementandthereferencepiezoelementthencanbemonitoredusingaWheatstonebridgeconfiguration .UsingthisPrC,chargedensitywavetransitionsofdepletedalphauranium(thickness0 .04mm)weremeasuredinthe31-tresistivemagnet(cell9,DCfacility,MagnetLab)andtheresult(Figure1,rightpanel)showsthreedistinctCDWtransitions(denotedasα

1,α

2,andα

3)andprovesthecapabilityofthisnewdilatometer .

Figure 1.schematicdiagramofpiezoresistivecantileverdilatometer(left)andchargedensitywavetransitionsinalpha-uraniumprobedbypiezoresisitivedilatometer(right) .

acKnowledGeMentssupportforthisworkwasprovidedbytheDOE/nnsaunderDE-FG52-06na26193 .Workwasperformed

attheMagnetLab,whichissupportedbynsFCooperativeagreementno .DMr-0654118andbythestateofFlorida .WorkatOccidentalCollegewassupportedbythensFunderDMr-0704406 .

ReFeRences1 . Park,J .-h .,et al .,Rev. Sci. Instrum .,80,116101(2009) .


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Stheabilitytomeasurespecificheatatveryhighmagneticfieldsrepresentsalong-standingobjectiveofMagLabuserprograms .Untilnow,suchmeasurementshavenotbeenpossibleintheshorterpulsedhigh-fieldmagnets .thereportbyy .Kohamaet al .describesanewaCspecificheatmeasurementtechniqueanditssuccessfulimplementationtodetectafieldinducedphasetransitionabove30tesla(t)inthespin-dimercompoundsr

3Cr

2O

8 .

FirstaCheatCapacityMeasurementinCapacitor-Bank-DrivenPulsedFieldsYoshimitsu Kohama (Magnet lab-lanl), christophe Marcenat (cea-Grenoble, institut nanosciences et cryogenie, spsMs-lateQs), Marcelo Jaime (Magnet lab-lanl)

intRodUctionspecificheat(C

p)athighfieldsisoneofthefundamentaltechniquesforunderstandingthemechanisms

andphysicsatplayincorrelatedelectronandmagneticmaterials .sofar,anumberofspecificheatmeasurementsinveryhighDCandlongpulsedmagneticfieldshavebeenreported .here,applyinganaC-C

p

techniquerunninginthekhzrange,wereportthedevelopmentofanewcalorimeterformeasurementinmid(250msec)pulsedmagneticfields .1

expeRiMentalWeusedruO

2barechips(stateoftheartInc .)asthermometersformid-pulsedmagneticfields,which

showamonotonic6-7%magnetoresistance .theruO2thermometerwasgluedtoasiplatewithGE7031

varnish .thesamplewasmountedontheruO2thermometerandgluedwithsilverpaint .aniCrfilmheater

withathicknessof10nm,~10kohm,wasdirectlydepositedonthesample .ByapplyingaCcurrentatafrequencyof~1khztotheheater,wecoulddetectthesecondharmonicoscillationwithanin-housedigitallock-insystem .asatestsample,wechoosesr

3Cr

2O

8andsisinglecrystals .Whilesishowsnophasetransition

inmagneticfieldsupto50t,sr3Cr

2O

8showsamagneticorderedstatebetweenH

c1≈30 .4andH

c2≈62t .2

ResUlts and discUssionFigure1showstheresultingaC-C

pdatainsr

3Cr

2O

8andsisinglecrystalsamples .sr

3Cr

2O

8showsa

sharppeakath≈Hc1

,whilethesisinglecrystaldoesnotshowanyanomaly .Inthefigureinset,thepeakalsoshowstemperaturedependence,whichisconsistentwiththepreviousmagnetocaloriceffect(MCE)studies .1althoughitisdifficulttocomparetheshapeofpeakwiththedatatakeninDCfields(redcurve)duetothetemperaturedifference,theDCfielddataalsoshowpeakasafunctionfield .asimilartemperature-suppressionoftheanomalyinC

p(h)wasrecentlyobservedinniCl

2-4sC(nh

2)

2 .3

Figure 1.Cp(h)measuredinsr

3Cr

2O

8

withanewaCcalorimeterformid-pulsedmagnets .


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S conclUsionsanewcalorimeterwasbuiltforaC-C

pmeasurementina50tcapacitor-bank-drivenmid-pulsedmagnet .

InitialresultsareconsistentwithpreviousDCmeasurements .additionaltestsareunderway .

acKnowledGeMentsWeareindebtedtoa .a .aczelandG .Lukeforprovidingthesr

3Cr

2O

8singlecrystalsusedforthethese

experiments .thisworkwassupportedbythenationalscienceFoundation,theU .s .DepartmentofEnergyandthestateofFlorida .

ReFeRences 1 .Kohama,y .,et al., Rev. Sci.Inst.,tobepublished(arXiv:1003 .3184) . 2 .aczel,a .a .,et al .,Phys. Rev. Lett .,103,207203(2009) . 3 .Zapf,V .s .,et al .,(unpublished) .

K . Koyama et al . report high temperature (> 350oC) differential thermal analysis (Dta) measurementsonthetechnologically important ferromagneticbinaryalloyMnBi inthe45tesla (t)hybridmagnet .aremarkablefielddependenceofthetemperature(T

t)atwhichthealloydecomposes intoamixtureof

paramagneticandliquidphasesisreported;ΔTt=80oCat45t .theobservedbehaviorismainlyattributed

thefield-inducedmagneticmomentoftheferromagneticphase .

DecompositiontemperatureofMnBito45teslaK. Koyama (tohoku U, institute for Materials Research); Y. Mitsui (tohoku U, iMR); e.s. choi (FsU, Magnet lab); Y. ikehara (tohoku U, iMR); K. watanabe (tohoku U, iMR); e. palm (FsU, Magnet lab)

intRodUctionscientistsallovertheworldusesteady,high-fieldmagnetstostudytheeffectsofhighmagneticfields

onmagneticphasetransitions,chemicalreactions,physicalprocesses,andsolidifications .Inordertostudythesephenomena,thermalanalysisunderhighmagneticfieldsisoneofthemostimportantexperiments .recently,Koyamaet al .observedthatthedecompositiontemperatureT

t(=355oC,628Katazeromagnetic

field)ofMnBiincreaseslinearlywithincreasingmagneticfieldsupto14tattherateof~2oC/t1 .thisresultindicatesthattheequilibriumdiagramoftheMn-Bibinarysystemisaffectedandcontrolledbyahighmagneticfield .thepurposeofthisstudyistoperformahigh-fieldDtaexperimentforferromagneticMnBiinhighmagneticfieldsandhightemperaturesbycombiningDtaandthe45-thybridmagnet(theworld’shigheststeadymagnetfield)togetthefirstdataonmagneticfieldeffectsondecompositionprocessandacorrespondingphasediagram .

Figure 1.typicalresultsofDtacurvesofMnBiundervariousmagneticfieldsupto45t .

Figure 2.PhasediagramofMnBi .theredsolidcirclesindicatettdeterminedbyDta .thedashedlinesareeyeguides .


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aDtasignalwasmeasuredforpowderMnBi(~100mg)inmagneticfieldsupto45tusingthe45t-hybridmagnetinthetemperaturerangeof20-500oC(293-773K) .themeasurementwasperformedintheheatingprocessattherateof~5 .oC/min .

ResUlts and discUssionFigures1and2showthetypicalresultsofDtacurvesofMnBiundervariousmagneticfieldsupto45t

andthephasediagram,respectively .themeltingpointofBi(TBi

)isnotchangedbymagneticfield .Ontheotherhand,thedecompositiontemperatureT

t(MnBiàMn

1 .08Bi+Liq .Bi)increaseslinearlywithincreasing

Bupto~20t,butthedataover20tdeviatefromthestraightline(~2oC/t) .Inaddition,wefoundthattheperitetictemperatureT

mincreaseswithincreasingB,whichisclearlyobservedover40t .thesephenomena

(thedeviationofTtfromthestraightlineandtheincreaseofT

m)areprobablyduetothefield-induced

magneticmomentofMn1 .08

Bi .WearenowcalculatingtheequilibriumdiagramoftheMn-Bibinarysysteminahighmagneticfieldtochecktheobtainedexperimentalresults .

conclUsionsthehF-Dtaexperimentwasperformedinhighmagneticfieldsupto45tforthefirsttime .theobtained

resultsclearlyshowthatthedecompositiontemperatureandperitectictemperatureofMn-Biincreasewithincreasingmagneticfield .

acKnowledGeMentsthisworkwaspartlysupportedbytheIketaniscienceandtechnologyFoundation .

ReFeRences 1 .K .Koyama,et al .,Mater. Trans .,48,2414-2418(2007) .


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gy this work reports both the first truly epitaxial pnictide films and bicrystals that enable the propertiesofgrainboundariestobemeasured .sadlyasimilardepressionofsuperconductingpropertiestothat

foundinthecupratesisseen,suggestingthatthispropertyisintrinsictosuperconductorsformedbydopingcarriersintoaparentnon-superconductingstate .

•thisworkwaspublishedinAppl. Phys. Lett.,95,21/212505(2009) .

CurrenttransportatGrainBoundariesinsuperconductingBa(Fe

1-xCo

x)

2as

2Bicrystals

J. Jiang, J. d. weiss, c. tarantini, a. xu, d. abraimov, a. polyanskii, a. Yamamoto, F. Kametani,e. e. Hellstrom, a. Gurevich, d. c. larbalestier (Mag lab-FsU); s. lee, c. M. Folkman, c. w. Bark, s. H. Baek, H. w. Jang, c. B. eom (U. of wisconsin); c. t. nelson, Y. Zhang, x. Q. pan (U. of Michigan)

intRodUctionGrainboundaries(GBs)transparenttocurrentareintrinsictonb-ti,nb

3snandMgB

2 .theferropnictide

superconductorshaveimportantapplicationproperties,namelytcupto55K,h

c2of100tesla(t)ormore,

strongvortexpinning,moderateanisotropy,andhirr

closetohc2,leavingopenonlythekeyquestion

whetherGBscantransmitcurrent .herewereporttheexplicitstudyofthisvitalproperty,usingextensivetransport,magneto-optical(MO),low-temperaturelaserscanningmicroscopy(LtLsM),andhighresolutiontransmissionelectronmicrocopy(hrtEM)investigationsofBa(Fe

1-xCo

x)

2as

2(Ba-122)epitaxialthinfilm

bicrystals .

Figure 1.Depressedsuperconductivityatthegrainboundary(GB)addsdissipation .(a)LtLsMimageofthelocalelectricfielddevelopedat6°GB .(b)Magneto-opticalimageandthecurrentstreamlinesturningduetotheblockingeffectof9°GB

Figure 2.DependenceofthecriticalcurrentdensityJc(12K,0 .5t,hperpendiculartothefilm)asafunctionoftheGBmisorientationangletheta .theinsertshowssummarydataforyBCOGBs .therapiddropinJgb(θ)withincreasingthetaintheBa-122bicrystalsexhibitsasimilarqualitativedependenceonthemisorientationangleθ .


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Epitaxial~350nmthickBa-122thinfilmsweregrownin-situon[001]tilt(100)srtiO3bicrystalsubstrates .

Four-circleX-raydiffractionshowedexcellentepitaxywithcube-on-cube,in-planeepitaxialrelationshipwiththesubstrates .WeperformeddetailedstudiesofthegrainandGBcriticalcurrentdensitiesJ

c(t,B)andJ

gb

(t,B)forthebicrystals .

ResUltsshowninFigure1arerepresentativeLtLsMandMOimagesof6oand9obicrystals,whichdemonstrate

thesignificantcurrent-blockingeffectofevenlow-angleGBs .theMOimageinFigure1bshowsthatthe9o[001]tiltGBcantransmitonlyabout10%oftheintragraincriticalcurrent .Figure2showsthatJ

gb(12K,0 .5t)

fallsoffbyanorderofmagnitudeasqincreasesfrom3to24o .thisqualitativebehaviorissimilartoJgb

(q)for[001]tiltGBsinyBCO .the3oGBinBa(Fe

1-xCo

x)

2as

2doesnotobstructsupercurrent,whileathigheranglesJ

gb

(q)becomesmuchsmallerthanthegrainJc .

conclUsionWehavedevelopedaprocessforgrowingpnictideBa-122singlecrystalthinfilms .J

gbacross[001]tilt

GBsofthinfilmBa(Fe1-x

Cox)

2as

2bicrystalsisstronglydepressed,similartohigh-t

ccuprates .Ourresultsraise

thequestionastowhetherweak-linkedGBsarecharacteristicofhigh-tcsuperconductingcompoundsdevelopedfromparentnon-superconductingstateswithcompetingorders,lowcarrierdensity,andunconventionalpairingsymmetry .

acKnowledGeMentsWorkattheMagnetLabwassupportedundernsFCooperativeagreementDMr-0084173,by

thestateofFlorida,andbyaFOsrgrantFa9550-06-1-0474 .WorkatUWwassupportedbyDOEgrantDE-FG02-06Er463 .WorkattheUniversityofMichiganwassupportedbytheDepartmentofEnergyundergrantDE-FG02-07Er46416 .

ReFeRences 1 .s .Lee,et al.,Appl. Phys. Lett .,95,212505(2009) .

It is now clear thatyBCO can be used not just for magnets of great strength at 4 K, but also to makemagnetsthatgeneratemoreusualfieldsof5to15tesla(t)inthetemperaturerangeupto65Kormore .thelimitstooperationaresetbytheirreversibilityfieldatwhichthecriticalcurrentdensitygoestozero .InthisrecentApplied Physics Letter, it isshownthattheverystrongpinningcentersthatnowcanbeputintoyBCOcoatedconductorsenhancetheirreversibilityfieldoverabroadangularrange,theeffectsbeinglargestathighertemperatureswheretheyareofgreatestpracticaluse .

•thisworkwaspublishedinAppl. Phys. Lett .,96,072506(2010) .

VortexLiquid-glasstransitionUpto60tinnano-engineeredCoatedConductorsM. Miura (Japan society for the promotion of science; superconductivity Research laboratory-international superconductivity technology center, Japan; Mpa-stc, lanl); s.a. Baily, B. Maiorov, l. civale, J.o. willis, K. Marken (Mpa-stc, lanl); t. izumi, K. tanabe, Y. shiohara (sRl-istec)

intRodUctionhigherirreversibilityfields(H

irr)increasetheupperboundforapplicationsofhighT

csupercon-

ductorsandcouldexpandtheirmarketpenetration1 .Weperformedthefirstpulsed-fieldstudiesoftheresistivetransitioninsuperconductingfilmsonflexiblemetalsubstrates,knownascoatedconductors(CC) .WeinvestigatedtheeffectofdisorderonH

irrandtheuppercriticalfield(H

c2)atdifferentorientations

ofthemagneticfield(H)foryBa2Cu

3O

y(yBCO)andBaZrO

3-nanoparticledispersedy

0 .77Gd

0 .23Ba

2Cu

3O

y

(yGdBCO+BZO) .

expeRiMentalthetwosamplesusedinthisstudyarebridgesof0 .5mm-thickCCofyBCOandyGdBCO+BZOgrown

byatrifluoroacetatemetalorganicdepositionprocessonIBaDmetaltemplates2 .alowaCcurrentdensity


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gy J~400a/cm2wasappliedalongthebridge .IntheDCfieldstudies(upto15t)arotatingstagewasusedtorotatetheCCwithrespecttoH .sixty-fivetpulsed-fieldmeasurementswereperformedwhilemaintaining

thesampleatfixedangles .InallcasesJ^H(maximumLorentzforce) .theHc2

andHirr

weredeterminedusing0 .9r

nand0 .01r

ncriteriarespectively,wherer

nisthenormalstateresistivity .

Figure 1temperaturedependenceof(a) H

c2

and(b)Hirr

withH||c,H||ab,andH||45°foryBCOandyGdBCO+BZOCCs .(c)normalizedresistivityvs .magneticfieldatH||cforyBCOCCusingbothpulsed(lines)andDCfields(circles) .(d)temperaturedependenceofg,foryBCO(opensymbols)andyGdBCO+BZO(solidsymbols)CCs,calculatedusingHab

c2 , Hc

c2

(diamonds)&H45 c2

, Hc c2

(stars) .

ResUlts and discUssionsincethesefilmsaregrownonmetalsubstrates,eddycurrentheatinginpulsedfieldswasaconcern .

BycomparingresultsobtainedusingpulsesofvariousmagnitudesandDCfields,heating

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