CMSP Seminar @ICTP Stasi Room: D. EFREMOV on Thursday 27 July at 11:30 am

[Condensed Matter Section]

Condensed Matter & Statistical Physics Seminar
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Thursday 27 July at 11:30- L. Stasi Seminar Room, ICTP Leonardo Bldg.

Speaker: Dmitri EFREMOV (IFW, Dresden, Germany)

"Superconductivity vs Bond State Formation in a Two Band Superconductor"

Abstract:

We discuss the interplay between superconductivity and formation of 
bound pairs of fermions (BCS-BEC crossover) in a 2D model of interacting 
fermions with small Fermi energy ϵF and a weak attractive interaction, 
which extends to energies well above ϵ_F. The 2D case is special 
because a two-particle bound state forms at arbitrary weak interaction, 
and already at weak coupling, one has to distinguish between the 
bound-state formation and superconductivity. We briefly review the 
situation in the one-band model and then consider two different two-band 
models: one with one hole band and one electron band and another with 
two hole or two electron bands. At ϵ_F≫E_0, where E_0 is the energy 
of the bound state of two particle in vacuum, the two models behave 
similar. But in the opposite case they behave differently: in the model 
with two hole/two electron bands, the instability temperature of 
formation of cooper pairs T_ins∼E_0/(logE_0/ϵ_F ), and the true 
superconducting critical temperature T_c∼ϵ_F, like in the one-band 
model. In between T_ins and T_c, the system displays a preformed pair 
behavior. In the model with one hole and one electron bands, T_c remains 
of order T_ins, and both remain finite at ϵ_F=0 and of the order of 
E_0. The preformed pair behavior still does exist in this model because 
T_c is numerically smaller than T_ins. All are most welcome to attend. 
http://indico.ictp.it/event/8286/