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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
Mechanism of spin-triplet superconductivity in Sr2RuO4 The unique Fermi surfaces...include the gaps with nodes, the breaking of time-reversal symmetry and d...
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 ....
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]....
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...
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...
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 ...
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...
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() Possible f -wave superconductivity in Sr2RuO4 ? H. Won1,2 and K. Maki2 2 Department of Physics, Hallym University, Chunchon 200-702, South ...
Coherence peak in the spin susceptibility from nesting in spin-triplet superconductors A pr
The superconductivity in Sr2 RuO4 has been revealed to be unconventional by many experiments; it is spintriplet2,3 , it breaks time-reversal symmetry4 ,...
Detailed Topography of the Fermi Surface of Sr2RuO4
Topography of the Fermi Surface of Sr2RuO4 ...the discovery of superconductivity in this compound...time reversal symmetry [7] and a number of ...