CMT Seminar: Denis I. Golosov – University of Copenhagen

CMT Seminar: Denis I. Golosov

Bar-Ilan University, Israel

Induced Hybridisation in the Falicov--Kimball model at T=0 and at finite temperatures

In an extended Falicov-Kimball model, an excitonic insulator phase can be stabilised at zero temperature. This is characterised by the (excitonic) long range order, and the stability of this phase can be probed with the help of a mean-field calculation of the low-energy collective excitation energies. With increasing temperature, the excitonic order parameter (interaction-induced hybridisation on-site, characterised by absolute value and phase) eventually becomes disordered, which involves fluctuations of both its phase and (at higher T) its absolute value. We show that the adequate description, as well as the phase-space integration measure, is provided by the SU(4) parametrisation on-site. In principle, his allows to describe both the lower-temperature regime where phase fluctuations destroy the long-range order, and the higher temperature crossover corresponding to an asymptotic vanishing of the absolute value of the hybridisation. This picture is also relevant in other contexts, including the Kondo lattice model.