Huikim

ICQMProgramon"Quantumcrystals,liquidsandgases"(June6—June10,2001)Schedule(Tentative):Title/Abstract:JasonAlicea:ArecipeforturninggrapheneintoarobusttopologicalinsulatorusingadatomsThe2007discoveryofquantizedelectricalconductanceinHgTequantumwellsdeliveredtheburgeoningfieldoftopologicalinsulators(TIs)itsfirstexperimentalconfirmation.
Subsequently,manythree-dimensionalTIshavebeenidentifiedamongnarrow-band-gapsemiconductorswithstrongspin-orbitcoupling(SOC),buttodateHgTeremainstheonlyknowntwo-dimensionalsysteminthisclass.
Despitemucheffort,difficultyfabricatingHgTequantumwellsandthecryogenictemperaturesrequiredtorealizetheTIphasehavehamperedtheirwidespreaduse.
InthistalkIwilldiscussarecentproposalforgeneratingarobustTIstateinamorereadilyavailabletwo-dimensionalsystem--graphene.
Specifically,IwilldescribehowendowinggraphenewithasmallconcentrationofindiumorthalliumadatomscaninduceaTIphasewithasubstantialband-gap(whichcanevenapproachroomtemperatureforthalliumcoverageaslowas~6%).
Engineeringsucharobusttopologicalphaseingraphenecouldpavethewayforanewgenerationofdevicesforspintronics,ultra-low-dissipationelectronics,anddecoherence-freequantuminformationprocessing.
ThequestforMajoranafermionsinsolidstatesystemsExchangestatistics,whichcharacterizeshowwavefunctionsevolveunderparticleinterchange,isoneofthemostfundamentalpropertiesofnatureandultimatelyunderliesmostcondensedmatterphenomena.
Interchangingordinarybosonsorfermions,forinstance,leavesthewavefunctioneitherunchangedorwithanextraoverallminussign.
ThestorybecomesmuchricherinaclassofsuperconductingstatessupportingexoticparticlesknownasMajoranafermions.
InterchangingMajoranafermionsproducesnotonlyaphase,butcanactuallytransformthewavefunctiontoafundamentallydifferentquantumstate.
Apartfromrevealingsomethingveryprofoundaboutnature,Majoranafermionsalsoholdpromiseforimplementingdecoherence-freequantuminformationprocessing.
ThistalkwillsurveyvariouspromisingproposalsforengineeringstatessupportingMajoranafermions,usingmaterialsrangingfromtopologicalinsulatorstomoreconventionalsystemssuchassemiconductorsandordinarysuperconductors.
Iwillalsodescribehow1DsystemscanbeusedtomeaningfullyexchangeMajoranafermions,inspiteofthatfactthatexchangestatisticsisusuallyviewedasill-definedin1D.
Shou-ChengZhang:TopologicalinsulatorsandsuperconductorsRecently,anewclassoftopologicalstateshasbeentheoreticallypredictedandexperimentallyobserved.
Thetopologicalinsulatorshaveaninsulatinggapinthebulk,buthavetopologicallyprotectededgeorsurfacestatesduetothetimereversalsymmetry.
Similarly,topologicalsuperconductorsorsuperfluidshavenoveledgeorsurfacestatesconsistingofMajoranafermions.
Inthistalk,Ishallreviewtherecenttheoreticalandexperimentalprogressinthefield,andfocusonanumberofoutstandingissues,includingthequantizedanomalousHalleffect,quantizedmagneto-electriceffect,thetopologicalMottinsulatorsandthesearchfortopologicalsuperconductors.
HuiZhai:Spin-orbitcoupledquantumgasesRecently,spin-orbitcoupledbosoncondensatehasbeenrealizedinNISTexperiment,andtherearemanyproposalstogeneratevarioustypesofspin-orbitcouplingincoldatomsetup.
Inthistalk,Iwilldiscussnewphysicsduetospin-orbitcouplinginquantumgasessystem.
Iwillpresentourtheoreticalresultsaboutgroundstateandfinitetemperaturepropertiesofspin-orbitcoupledinteractingbosons.
Atzerotemperaturethissystemexhibitstwodifferentphases,theplanewavephaseandthestripephase.
Atfinitetemperature,meltingofstripeordergivesrisetoanovelphase,thatis,bosonpairedsuperfluidwhichsupportsfractionalizedvortices.
Ishallpresentthephasediagramofthissystemin6,Mon7,Tue8,Wed9,Thu10,Fri9:30-10:30JasonAliceaHuiZhaiYong-BaekKimSrinivasRaghuFaWang10:30-10:45BreakBreakBreakBreakBreak10:45-11:45JasonAliceaFaWangYong-BaekKimSrinivasRaghuYingRan14:00-15:00Shou-ChengZhangKaiSunChiZhangHongYao15:00-17:00DiscussionDiscussionDiscussiontermsoftemperature,interactionandanisotropyofspin-orbitcoupling.
IshallalsobrieflydiscussBEC-BCScrossoverofspin-orbitcoupledFermigasacrossaFeshbachresonance.
References:1.
ChunjiWang,ChaoGao,Chao-MingJianandHuiZhai,Phys.
Rev.
Lett.
105,160403(2010).
2.
Chao-MingJianandHuiZhai,tobepublished3.
Zeng-QiangYuandHuiZhai,arXiv:1105.
2250FaWang:Functionalrenormalizationgroupstudiesofiron-basedhighTcsuperconductorsIwillbrieflyreviewthephysicsofiron-basedsuperconductorsanddiscussourapproach,thefunctionalrenormalizationgroupmethod,tothepairingprobleminthesesystems.
Thismethod,despitesignificanttechnicalchallenges,isinprincipleunbiasedandsuitableforthestudiesofelectronicinstabilitiesofFermiliquidswithweaktointermediatecorrelations.
Applyingthismethodwefoundthatforiron-pnictidessuperconductorsthedominantpairinginstabilityisthes_{\pm}pairing,apairingorderparameterwithsignchangeinmomentumspacebutisatrivialrepresentationofthespacegroup.
Howeverwefoundthatdetailsofthepairingorderparameter,e.
g.
whethertherearegapnodesonFermisurfaces,variesamongdifferentiron-pnictides.
Iwillalsodiscusstheremainingchallengesinthisfield,e.
g.
theexperimentaldetectionofthepredictedpairingorderparameter.
KaiSun:Emergingconformalsymmetryandzero-energyedgemodesinisostaticlatticesRigiditytransitionsinelasticsystemshavebeenthefocusofintensivestudies.
Inthetheoreticalunderstandingofthesetransitions,theideaofisostaticityhasbeenfoundtoplayanimportantroleandcapturestheessentialphysicsinmanydifferentsystems,suchasrandompackings,polymernetworks,etc.
Inthistalk,Iwillfirstprovideabriefintroductiontotheideaofisostaticityandthenpresentourrecentstudiesonanewclassofisostaticsystemsintwodimensions.
Oneofthekeyfeaturesofthesesystemsistheexistenceofalargenumberofzero-energyvibrationalmodeslocalizedattheedges.
Inthephenomenologicallevel,theemergenceoftheseedgemodesisaclassicalanalogytosometopologicalstatesofmatterstudiedinquantumsystems.
However,differentfromthequantumsystems,theseedgemodeshereareprotectedbyanemergingconformalsymmetryinthelow-energyeffectivetheory.
Atlongdistance,thisemergingsymmetryresultsinuniversalbehaviorsforallisostaticsystemsinthisuniversalityclass.
However,intheshortdistancelimit,subleadingcorrections,knownasthedangerousirrelevantterms,breaktheemergingconformalsymmetryandleadstononuniversalbehaviorssensitivetomicroscopicdetails.
Thiscrossoverwillalsobeaddressed.
Yong-BaekKim:TopologicalPhasesinCorrelatedSystemswithStrongSpin-OrbitCouplingIthasrecentlybeenrecognizedthat5dtransitionmetaloxidesmayprovideanewavenuefortheemergenceofnovelelectronicphases.
Inthesesystems,thestrengthoftheinteraction,effectiveband-width,andspin-orbitcouplingmaybecomparable.
Wediscusstheoryofpossibletopologicalinsulators,spinliquids,andotherrelatedphasesthatcouldberealizedinsuchsystems.
Wealsodiscusspotentialcandidatematerialsforthesephases.
SrinivasRaghu:SuperconductivityintherepulsiveHubbardmodel:anasymptoticallyexactweakcouplingsolutionWestudythephasediagramoftheHubbardmodelinthelimitwhereU,theonsiterepulsiveinteraction,ismuchsmallerthanthebandwidth.
WepresentanasymptoticallyexactexpressionforT$_c$,thesuperconductingtransitiontemperature,intermsofthecorrelationfunctionsofthenon-interactingsystemwhichisvalidforarbitrarydensitiessolongastheinteractionsaresufficientlysmall.
OurstrategyforcomputingT$_c$involvesfirstintegratingoutalldegreesoffreedomhavingenergyhigherthananunphysicalinitialcutoff$\Omega_0$.
Then,therenormalizationgroup(RG)flowsoftheresultingeffectiveactionarecomputedandT$_c$isobtainedbydeterminingthescalebelowwhichtheRGflowsintheCooperchanneldiverge.
WeprovethatT$_c$isindependentof$\Omega_0$.
ChiZhang:UnusualConductivityofa2DHoleWignerCrystalInUltrahighMagneticFieldsInanewtypeofcarbon-doped,highholedensity(p=1.
9*1011cm-2),highmobility(mu>1x106cm2/Vs)quantumwells,wediscoveredareentrantinsulatingphase(PI)aroundfillingfactornuortedthereentrantPIaroundnu=1/3FQHEstateindilute2DHS[1]andaroundnu=1/5FQHEindilute2DES[2].
InarangeofultrahighmagneticfieldB~30-42T,wesystematicallymeasuredthemagnetoconductance(sigmaxx)inaCorbinoconfiguration,andtwomajorfindingsemerge:1)at1/5,aPIprevailsatT100mK;and,2)xxshowsaremarkableλ-shapeasafunctionof1/T.
AboveacriticalTc~200mK,sigmaxxincreasesexponentiallywith1/T;andbelowTc,sigmaxxdecreasesexponentiallywith1/T.
Weinterprettheλ-shapeasthelong-sought-aftersignatureofasuperfluid-insulatortransition.
DifferentialconductivityinthePIphasesshowsstrongnonlinearresponse,indicatingapinned-tosliding-Wignercrystaltransitiondrivenbyelectricalfield.
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Sajoto,Y.
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TsuiandM.
Shayegan,PhysicalReviewLetter70,2321(1993).
FaWang:Schwingerbosonspinliquidstatesonhoneycomblattice:projectivesymmetrygroupanalysisandcriticalfieldtheoryMotivatedbythenumericalevidenceofagappedspinliquidinthehoneycombHubbardmodel[Mengetal.
Nature464,847(2010)],weanalysepossibleZ_2spinliquidswithgappedbosonicspinonscoupledtoZ_2gaugefieldonhoneycomblatticewithintheSchwingerbosonformalism.
BytheprojectivesymmetrygroupmethodwefindthatthereareonlytworelevantZ_2spinliquidsonhoneycomblatticewithdifferent(zeroor$\pi$)gaugefluxintheelementalhexagon.
Thezero-fluxstateseemstobeagoodcandidateforthenumericallyobservedspinliquid.
ItcanacquirecollinearAFMNeelorderviaacontinuousO(4)transition.
InthecriticalfieldtheoryofthistransitionthecouplingofbosonicspinonstotheHiggsfieldcontainscubicpowersofspatialderivatives,thereforedoesnotbreakhoneycomblatticesymmetryandallowsforacontinuoustransitiontoacommensuratecollinearNeelorder.
Wewillalsodiscussseveralobservablefeaturesofthisspinliquid.
YingRan:Z2spinliquidandchiralanti-ferromagneticphaseonhoneycomblattice.
Followingtheprevioustalk,Iwilldiscussthesamephasediagramfoundbyquantummontecarloonhoneycomblattice[Mengetal.
Nature464,847(2010)].
Weuseadifferentmethod:Schwinger-fermionapproach,andproposeoneparticularstate,sublatticepairingstate,asthespinliquidstatefoundinthephasediagram.
Inourapproach,boththeMotttransitionandthemagneticphasetransitionarestudied.
Wepredictionofanovelhidden-phase:chiralanti-ferromagneticphaseinthesamephasediagram.
Surprisingly,weshowthatsublatticepairingstateisidenticaltothezero-fluxstatediscussedbyFaWang.
ThisisthefirsttimethatadualitybetweenSchwinger-fermionandSchwinger-bosonrepresentationsisobtained.
HongYao:TBA