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1、AbsenceofBCSCondensationofAtomsinaRepulsiveFermiGasofAtomsFuxiangHan,HailingLi,MinghaoLei,andEWuDepartmentofPhysics,DalianUniversityofTechnology,Dalian,Liaoning116024,China(Dated:February2,2008)PossibleBose-EinsteincondensationofmoleculesandBardeen-Cooper-Schrieffer(BCS)conden-sationofCooperpair
2、sofatomsinanultracoldFermigasofatomswitharepulsivetwo-bodyinteractionarestudiedbyusingthepathintegralrepresentationofthegrandpartitionfunction.Fromtheself-consistentequationsobtainedinthepresentworkfortheorderparameters,wehavefoundthatBCScondensationofatomscan’toccurinsuchaFermigasofatomsandtha
3、ttheconden-sateobservedexperimentallyiscomposedofcondensedmoleculesorpossiblyofpreformedCooperpairs.Tosubstantiateourconclusionsfromtheself-consistentequationsfortheorderparameters,theeffectiveatom-atominteractionmediatedthroughmoleculeshasalsobeencomputedwiththeFoldy-Wouthuysentransformationand
4、hasbeenfoundtoberepulsive,whichimpliesanetrepulsivetwo-bodyinteractionbetweenatomsandhencetheabsenceofBCScondensationofatoms.PACSnumbers:03.75.Ss,05.30.Fk,67.90.+zTheexperimentalrealization[1]ofanultracoldFermiandannihilationoperatorsofamoleculeofmomentum†gasofatomsmarksthebeginningofaneweraoft
5、hepandenergy2(ν−µ),ckσandckσarecreationandan-scientificresearchondegeneratequantumFermigases.nihilationopperatorsofafermionicatomofmomentumSincethen,Bardeen-Cooper-Schrieffer(BCS)condensa-k,spinσ,andenergyǫ=~2k2/2m,U(>0)isthektionoffermionicatomsandBose-Einsteincondensationstrengthofthetwo-bodyin
6、teractionbetweenatoms,gis(BEC)ofdiatomicmoleculesoftheseatomsaswellasthetheeffectiveatom-moleculecouplingconstant,andNiscrossoverbetweentheBCSandBECregimeshavebeentheaveragenumberofatoms.Herethespinupandspinunderintensivestudyboththeoretically[2,3,4,5,6,7,8]downactuallyrepresenttwodifferenthyperfi
7、nelevelsofandexperimentally[9,10,11,12,13,14],withtheatoms.HerewehaveassumedthatthereareonlytwoBCS-BECcrossoverregimebeingeasilyreachedwiththecomponentsinthegas.magnetic-fieldFeshbachresonance[10].NoticethatthenumberofatomsNinthesy
