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Опубликовано
2012-11-14
Опубликовано на SciPeople2013-08-23 15:38:28
ЖурналElsevierLtd.Allrightsreserved
True, quasiandunstableNambu–Goldstonemodesofthetwo-dimensional Bose–Einsteincondensedmagnetoexcitons
Solid StateCommunications155(2013)57–61
Аннотация
The collectiveelementaryexcitationsoftwo-dimensionalmagnetoexcitonsinaBose–Einsteincon-
densate(BEC)withwavevector k ! ¼ 0 wereinvestigatedintheframeworkoftheBogoliubovtheoryof
quasi-averages.TheHamiltonianoftheelectronsandholeslyinginthelowestLandaulevels(LLLs)
containssupplementaryinteractionsduetovirtualquantumtransitionsoftheparticlestotheexcited
Landaulevels(ELLs)andback.Asaresult,theinteractionbetweenthemagnetoexcitonswith k ! ¼ 0
does notvanishandtheirBECbecomesstable.Theenergyspectrumcontainsonlyonegapless,true
Nambu–Goldstone(NG)modeofthesecondkindwithdependence oðkÞ k2 at smallvalues k
describingtheoptical-plasmon-typeoscillations.Therearetwoexciton-typebranchescorresponding
to normalandabnormalGreen’sfunctions.Bothmodesaregappedwithroton-typesegmentsat
intermediaryvaluesofthewavevectorsandcanbenamedasquasi-NGmodes.Thefourthbranchisthe
acousticalplasmon-typemodewithabsoluteinstabilityintheregionofsmallandintermediaryvalues
of thewavevectors.Allbrancheshaveasaturation-typedependenciesatgreatvaluesofthewave
vectors.ThenumberandthekindofthetrueNGmodesareinaccordancewiththenumberofthe
brokensymmetryoperators.