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1、epldraftSpin-wavespectraofakagomestripeA.Donkov1andA.V.Chubukov21Max-Planck-Institutf¨urPhysikKomplexerSysteme,D-01187Dresden,Germany2DepartmentofPhysics,UniversityofWisconsin,Madison,WI53706,USAPACS75.10.Pq–SpinchainmodelsPACS75.30.Ds–SpinwavesAbstract.-Westudygroundstatedegeneracyandspin
2、-waveexcitationsina1DversionofaKagomeantiferromagnet–aHeisenbergantiferromagnetonaKagomestripe.Weshowthatfornearest-neighborinteraction,theclassicalgroundstateisinfinitelydegenerate.Foranyspinconfigurationfromthedegenerateset,theclassicalspin-wavespectrumcontains,inadditiontoGoldstonemodes,a
3、branchofzeroenergyexcitations,andazeromodeinanotherbranch.Wedemonstratethattheinteractionsbeyondnearestneighborsliftthedegeneracy,eliminateazeromode,andgiveafinitedispersiontoformerlyzero-energybranch,leavingonlyGoldstonemodesaszero-energyexcitations.Inthelastfewyears,therehasbeenarevivalof
4、in-anenergycosttolocalrotations.terestinthestudiesoffrustratedspinsystems.OneofMostofrecentworkonKagome-typesystemswasde-themostintriguingaspectsofspinfrustrationistheexis-votedto3DversionofaKagomeantiferromagnet,whichtence,inmanycases,ofextrazeromodesintheexcitationisanantiferromagnetofth
5、epyrochlorelattice[7].Lessat-spectrum,inadditiontoGoldstonemodesrelatedtothetentionwasgiventoan“opposite”1Dversion,whichisanbreakingofacontinuoussymmetry.ThesezeromodesareantiferromagnetonaKagomestripe.Thisisathree-chainoftenassociatedwiththelocaldegeneracyofaclassicalstructure,consistingo
6、foftop/bottomsharinghexagonsgroundstateofafrustratedsystemwithshort-rangein-(Fig.1b).Likeits2Dparent,aKagome-stripeantifer-teractionsbetweennearest-neighbors,andareliftedeitherromagnetcanbeobtainedfromathree-chaintriangularbyfluctuations,thermalorquantum,orbylonger-rangeantiferromagnetbyrem
7、oving1/6ofthespins(Fig.1a).interactionswhichincludesecond,third,etcneighbors[1].Theexistinganalytical[8,9]andnumerical[10,11]worksfocusedonS=1/2andprimarilyaddressedtheissueThemostprominentexampleofasystemwithextraofaspin-disorderedstatewithgappedspin-triplete
