Interplay between single-particle and collective features in the boson fermion model
- Centre de Recherches sur les Tres Basses Temperatures, CNRS, 38-042 Grenoble Cedex 9 (France)
We study the interplay between the single-particle and fermion-pair features in the boson fermion model, both above and below the transition temperature T{sub c}, using the flow equation method. Upon lowering the temperature the single-particle fermionic spectral function (a) gradually develops a depletion of the low-energy states (pseudogap) for T*>T>T{sub c} and a true superconducting gap for T<T{sub c} and (b) exhibits a considerable transfer of spectral weight between the incoherent background and the narrow coherent peak(s) signifying long-lived quasiparticle features. The Cooperon spectral function consists of a {delta}-function peak, centered at the renormalized boson energy {omega}=E-tilde{sub q} and a surrounding incoherent background which is spread over a wide energy range. When the temperature approaches T{sub c} from above, this peak for q=0 moves to {omega}=0, so that the static pair susceptibility diverges (Thouless criterion for the broken symmetry phase transition). Upon decreasing the temperature below T{sub c} the Cooperon peak becomes the collective (Goldstone) mode E{sub q}{proportional_to} vertical bar q vertical bar in the small-momentum region and simultaneously splits off from the incoherent background states which are expelled to the high-energy sector vertical bar {omega} vertical bar {>=}2{delta}{sub sc}(T). We discuss the smooth evolution of these features upon approaching T{sub c} from above and consider its feedback on the single-particle spectrum where a gradual formation of damped Bogoliubov modes (above T{sub c}) is observed.
- OSTI ID:
- 20662173
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 70, Issue 18; Other Information: DOI: 10.1103/PhysRevB.70.184503; (c) 2004 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
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