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Time-Reversal Symmetry Breaking Superconductivity in Sr2RuO4

SubmittedtoNature1

Time-ReversalSymmetryBreakingSuperconductivityinSr2RuO4

arXiv:cond-mat/9808159v1 [cond-mat.supr-con] 14 Aug 1998

G.M.Luke∗,Y.Fudamoto∗,K.M.Kojima∗,http://www.sodocs.net/doc/8f56d5e9551810a6f5248659.html rkin∗,J.Merrin∗,B.Nachumi∗,Y.J.Uemura∗,Y.Maeno†,Z.Q.Mao†,Y.Mori†,H.Nakamura‡,M.Sigrist§

Dept.ofPhysics,ColumbiaUniversity,NewYork,NY10027,U.S.A.†

Dept.ofPhysics,KyotoUniversity,Kyoto606-8502,Japan.‡

Dept.ofMaterialScienceandEngineering,KyotoUniversity,Kyoto606-8501,Japan.§

YukawaInstututeforTheoreticalPhysics,KyotoUniversity,Kyoto606-8502,Japan.

Inadditiontoitsimportanceforexistingandpotentialapplications,superconductivity[1]isoneofthemostinterestingphenomenaincondensedmatterphysics.Althoughmostsuperconductingmaterialsarewell-describedinthecontextoftheBardeenCooperandSchrieffer(BCS)theory[2],considerableefforthasbeende-votedtothesearchforexoticsystemswhosenovelpropertiescannotbedescribedbytheBCStheory.Conventionalsuperconductorsbreakonlygaugesymmetrybyselectingadef-initephasefortheCooperpairwavefunction;asignatureofanunconventionalsupercon-ductingstateisthebreakingofadditionalsymmetries[3].Evidenceforsuchbrokensymmetriesincludeanisotropicpairing(suchasd-waveinthehigh-Tccuprates)andthepresenceofmultiplesuperconductingphases(UPt3andsuperfluid3Wehaveper-formedmuonspinrelaxationmeasurementsofSr2RuO4andobserveaspontaneousinternalmagneticfieldappearingbelowTc.Ourmeasurementsindicatethatthesupercon-ductingstateinSr2RuO4ischaracterizedbybrokentimereversalsymmetrywhich,whencombinedwithsymmetryconsiderationsin-dicatethatitssuperconductivityisofp-wave(odd-parity)type,analagoustosuperfluid3

He.DespitethestructuralsimilaritywiththehighTccuprates,theoriginoftheun-conventionalsuperconductivityinSr2RuO4isfundamentallydifferentinnature.

Sr2RuO4,whichisisostructuraltothehigh-TccuprateLa1.85Sr0.15CuO4,istodatetheonlyknownlayeredperovskitesuperconductorwhichdoesnotcontaincopper.Althoughfirstsynthesizedinthe50’s,[5]itssuperconductivitywasonlyfoundin

1994[6];Tc’sofearlysampleswereroughly0.7KbuthaveincreasedtoTc=1.5Kinrecenthighqualitysinglecrystals[7].Despiteitslowtransitiontemperature,Sr2RuO4isofgreatinterestasthereisgrowingevidenceforanunconventionalsupercon-ductingstate.Inthissystem,strongcorrelationef-fectsenhancetheeffectivemassseeninquantumoscillation[8]andPaulispinsusceptibilitymeasure-ments,inthesamewayasin3CombiningthisfeaturewithSr2RuO4’sexpectedtendencytodisplayferromagneticspinfluctuations,RiceandSigrist[10],andlaterBaskaran[11]arguedthatthepairinginSr2RuO4couldbeofoddparity(spintriplet)type.ThestrongsuppressionofthesuperconductingTcbyevennon-magneticimpuritiessuggestsnon-s-waveSpecificheat[12]andNMR1/T1[13]mea-surementsindicatethepresenceofalargeresidualdensityofstates(RDOS)atlowtemperatures(wellwithinthesuperconductingstate);inhighqualitysamples,thisRDOSasT→0seemstoapproachhalfofthenormalstatevalue.Severalauthors[14,15]haveproposedso-callednon-unitaryp-wavesuper-conductingstatesforSr2RuO4toaccountforthisRDOSaswellastheabsenceofaHebel-SlichterpeakinNMRmeasurements[13].AfiniteRDOSisnotauniquesignatureofunconventionalsuperconductiv-ity;forexampleitisobservedinso-calledgaplesssuperconductorswithisotropics-wavepairingasare-sultofimpurityscattering(althoughthisisunlikelyinthespecificcaseofSr2RuO4wherethefiniteRDOSapparentlyremainsinthecleanestsamples).Itcouldalsobeexplainedwithamulti-bandhypothesis[16]wheredifferentgapsareassociatedwithtwotypesofbands.Therefore,furtherstudiesarerequiredforadefinitivedeterminationofthepairingsymmetryinSr2RuO4.

Oneaspectofthepairingsymmetry,thebreakingoftimereversalsymmetry(TRS)canbeprobeddi-rectly.Ifthesuperconductingstatehasadegeneraterepresentation(asispossibleforsometripletsuper-conductingstates)thenTRScanbebroken,whereasitcannotbebrokenfornon-degeneraterepresenta-tions(thecaseforallsingletstates).Whenspinor-bitcouplingissmall,thepairwavefunctioncanbewrittenasaproductoftheorbitalpartandthespinpart.Non-zeroangularmomentumofeithertheor-bitalorthespinpartcouldresultinTRSbreaking,althoughtherearemanysuchcaseswithconservedTRS,suchasd-wavestatesinthehigh-Tccuprates.TRSbreakingisalsopossibleinthecaseofstrongspinorbitcoupling.Ingeneral,pairingstatescanbefurtherclassifiedintermsofgapfunctionsattachedtoirreduciblerepresentationsofapointgroupforagivencrystallatticesymmetryofthesystem[3].TRS

Mechanism of spin-triplet superconductivity in Sr2RuO4
include the gaps with nodes, the breaking of time-reversal symmetry and d...Shortly after the discovery of the superconductivity in Sr2 RuO4 , it was ...
Phase-sensitive tests of the pairing state symmetry in Sr2RuO4
The former indicate a time-reversal symmetry breaking below the transition ...providing a plausible scenario for spinsinglet superconductivity in Sr2 RuO4 ....
Ferromagnetism and triplet superconductivity in the two-dimensional Hubbard model
However there is a consensus that the superconductivity in Sr2 RuO4 arises ...time-reversal symmetry-breaking superposition of the two 3 1 max max 1 0...
Non-Fermi-Liquid Behavior in Sr2RuO4 with Nonmagnetic Impurities
Sr2 RuO4 breaks down in the vicinity of the critical impurity concentration ...translational symmetry breaking, characteristic of unconventional superconductivity ...
The penetration depth in Sr2RuO4 Evidence for orbital dependent superconductivity
penetration depth in Sr2RuO4 Evidence for orbital dependent superconductivity ..., which was attributed to pairing with broken time reversal symmetry [5]....
Inelastic neutron scattering study of magnetic excitations in Sr2RuO40206304
It is further established that superconductivity in Sr2 RuO4 is made of spintriplet Cooper pairs and breaks time-reversal symmetry [2, 4]. The strongest...
Cooper Pairs with Broken Parity and Time-Reversal Symmetries in D-wave Superconductors
Sr2 RuO4 [12], (TMTSF)2 X [13], ...singlet superconductivity, which is (1) in a magnetic...breaking time-reversal symmetry, has to change all...
Detailed Topography of the Fermi Surface of Sr2RuO4
Topography of the Fermi Surface of Sr2 RuO4 C....time reversal symmetry [7] and a number of ...superconductivity in real depth: of all known ...
Horizontal line nodes in superconducting Sr2RuO4
Horizontal line nodes in superconducting Sr2 RuO4 ...superconductivity, the superconducting phase of ...breaking of time reversal symmetry at Tc , which...
Interband Coulomb Interaction and Horizontal Line Nodes in Triplet Superconductor Sr$_2$RuO
the horizontal line nodes in triplet superconductor, Sr2 RuO4 , is proposed...The superconductivity breaks the time-reversal symmetry, as indicated by ?SR...