$S$-wave pairing symmetry in non-centrosymmetric superconduc

The alloys of non-centrosymmetric superconductor, Re$_3$W, which were reported to have an $\alpha$-Mn structure [P. Greenfield and P. A. Beck, J. Metals, N. Y. \textbf{8}, 265 (1959)] with $T_\mathrm{c}=9 $K were prepared by arc melting. The ac susceptibil

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aS-wavepairingsymmetryinnon-centrosymmetricsuperconductorRe3WJingYan,LeiShan,QiangLuo,WeihuaWang,Hai-HuWen NationalLaboratoryforSuperconductivity,InstituteofPhysicsandBeijingNationalLaboratoryforCondensedMatterPhysics,ChineseAcademyofSciences,P.O.Box603,Beijing100080,P.R.China

The alloys of non-centrosymmetric superconductor, Re$_3$W, which were reported to have an $\alpha$-Mn structure [P. Greenfield and P. A. Beck, J. Metals, N. Y. \textbf{8}, 265 (1959)] with $T_\mathrm{c}=9 $K were prepared by arc melting. The ac susceptibil

1Introduction

Veryrecentlythescienti ccommunityhaspaidalotofattentioninunder-standingthesupercondictivityofthenon-centrosymmetricsuperconductors,sincethesuperconductingpropertiesofsuchmaterialsareexpectedtobeun-conventional[1,2,3,4,5,6,7].Inalatticewithinversionsymmetry,theorbitalwavefunctionofthecooperpairhasacertainsymmetryandthespinparingwillbesimplyineitherthesingletortripletstate.Thenoncentrosymmetryinthelatticemaybringacomplexitytothesymmetryoforbitalwavefunc-tion.Thise ectwiththeantisymmetricspin-orbitalcouplinggivesrisetothebrokenofthespindegeneracy,thustheexistenceofthemixtureofspinsingletandtripletmaybecomepossible[2,5].Sotheremightbesomethingunconventional,suchasspintripletpairingcomponent,existinginthenon-centrosymmetricsuperconductors.Recently,aspin-tripletpairingcomponentwasdemonstratedinLi2Pt3Bbothbypenetrationdepthmeasurement[4]andnuclearmagneticresonance(NMR)[5],aswasascribedtothelargeatomicnumberofPtwhichenhancesthespin-orbitcoupling.

Re3Wisoneoftherheniumandtungstenalloys’family.Uptonow,twosuperconductingphasesofRe3WwerereportedwithTc～9K[8]andTc～7K[9].Bothphasesbelongtotheα-Mnphase(A12,spacegroupI¯43m)[10],whichhasanon-centrosymmetricstructure.Moreover,atomicnumbersofReandWare75and74,respectively,beingclosetothatofPt.Therefore,similarspin-tripletpairingcomponentasthatinLi2Pt3BareexpectedinRe3W.Mostrecently,itwasfoundthatthesuperconductingphaseofRe3WwithTc～7Kisaweak-couplings-waveBCSsuperconductorbybothpenetrationdepth[9]andAndreevre ectionmeasurements[11].

The alloys of non-centrosymmetric superconductor, Re$_3$W, which were reported to have an $\alpha$-Mn structure [P. Greenfield and P. A. Beck, J. Metals, N. Y. \textbf{8}, 265 (1959)] with $T_\mathrm{c}=9 $K were prepared by arc melting. The ac susceptibil

Inthispaper,wereportthemeasurementsoftheacsusceptibilityandlow-temperaturespeci cheatofRe3Walloys.Boththemeasurementsimplythatoursampleshavetwosuperconductingphaseswithcriticaltemperaturesnear9Kand7K,respectively,andthehightemperaturephasenear9Kaccountsfornearly78%-87%intotalvolume.Thespeci cheatdatacanbe ttedverywellbythesimpletwo-componentmodel,whichisbasedontheisotropics-waveBSCtheory.Furthermore,alinearrelationshipisfoundbetweenthezero-temperatureelectronicspeci cheatcoe cientandtheappliedmagnetic eld.TheseresultssuggestthattheabsenceoftheinversionsymmetrydoesnotresultinnovelpairingsymmetryinRe3W.

2Experiment

TheRe3WalloysarepreparedbyarcmeltingtheReandWpowders(purityof99.9%forboth)withnominalcomponent3:1inaTi-getteredargonatmo-sphere.Normally,theobtainedalloyisahemisphereinshapewithadimensionof5mm(radius)×5mm(height).Somepiecesofthealloyhadbeencutfromtheoriginalbulk(e.g.sample 1andsample 2).Theacsusceptibilityofthesesampleshasbeenmeasuredatzerodcmagnetic eldtoidentifytheirsuper-conductingphases,whereas,allofthemhavetwosuperconductingtransitionsatabout9Kand7K,asshowninFig.1.Thespeci cheatwasmeasuredbyaPhysicalPropertyMeasurementSystem(PPMS,QuantumDesign).Thedataatamagnetic eldwereobtainedwithincreasingtemperatureafterbeingcooledin eldfromatemperaturewellaboveTc,namely, eldcoolingprocess.

The alloys of non-centrosymmetric superconductor, Re$_3$W, which were reported to have an $\alpha$-Mn structure [P. Greenfield and P. A. Beck, J. Metals, N. Y. \textbf{8}, 265 (1959)] with $T_\mathrm{c}=9 $K were prepared by arc melting. The ac susceptibil

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T (K)

Fig.1.(Coloronline)Temperaturedependenceofacsusceptibilityonsample 1underdi erentdcmagnetic elds,withac eldh=1Oeandfrequencyf=333Hz.3Resultsanddiscussion

Thetemperaturedependenceofacsusceptibility(χ=χ′+iχ′′)atdi erentdcmagnetic eldsfrom0Tto7TisshowninFig.1.OnecanseethattwodistinctsuperconductingtransitionsoccuratTc1～9andTc2～7Kinχ′(T)curveatH=0[Fig.1(b)],anddoublepeaksinχ′′(T)showupatthecorrespondingtemperatures.Thesetwophasesareconsistentwiththepreviousreportsinwhichtheyareproofedtobenon-centrosymmetric[8,9].Thepeaksofχ′′shifttolowertemperaturesasthemagnetic eldincreases,showingthecontinuoussuppressionofsuperconductivitybythemagnetic eld.Thelow-Tpeakshiftstolowertemperaturesmoreslowlythanthehigh-Tone,indicatingdistinctbehaviorsoftheuppercritical eldsinthesetwosuperconductingphases.As

The alloys of non-centrosymmetric superconductor, Re$_3$W, which were reported to have an $\alpha$-Mn structure [P. Greenfield and P. A. Beck, J. Metals, N. Y. \textbf{8}, 265 (1959)] with $T_\mathrm{c}=9 $K were prepared by arc melting. The ac susceptibil

)2C/T (mJ/mol K 04080120160

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T (K)

Fig.2.(Coloronline)Speci cheatdataofsample 2plottedasC/TversusT2atvarious elds.

Hincreasesto～7T,theχ(T)curvesarecompletely at,showingnosignofsuperconductingtransition.Similarresultswereobtainedons …… 此处隐藏：12193字，全部文档内容请下载后查看。喜欢就下载吧 ……