THE IMPACT OF THE MASS IMBALANCE ON OPTICAL PROPERTIES OF EXCITON SYSTEMS IN THE CONDENSATION STATE

Abstract

In this research, the optical properties of the exciton systems in the condensed state are considered through the real part spectrum of the optical conductivity in the extended Falicov-Kimball model in the presence of phonons. Applying the Hartree-Fock approximation and the Kubo linear response theory, a set of equations determining the excitonic condensation order parameter and the real part of the optical conductivity are found. Numerical results investigating the real part of the optical conductivity affected by the mass imbalance show that in the phonon assistance, a single-peak appears in the optical conductivity spectrum in the excitonic condensation state when the mass imbalance is sufficiently small. The peak occurs at a frequency twice the exciton condensation order parameter. Decreasing the mass imbalance, the peak position moves to the right indicating the stabilization of the excitonic condensation state. When the electron-phonon coupling is large enough, the BCS-type condensation prevails even if the mass imbalance is large.