Bipolaron formed through electron-hole excitation

TL;DR

This paper explores the formation and properties of bipolarons via electron-hole excitations in a Yukawa-coupled fermion system, revealing their Fermi-liquid behavior and the influence of bosonic momentum on their characteristics.

Contribution

It provides a detailed theoretical analysis of bipolaron formation through electron-hole excitations, including the effects of Yukawa coupling and bosonic momentum on their properties.

Findings

Bipolaron exhibits Fermi-liquid features under suppressed long-range interactions.

Bosonic momentum influences the mass of the boson propagator and the gap function.

Critical temperature decreases in the weak-coupling regime, as shown by the Thouless criterion.

Abstract

We investigate the electronic properties and electron correlations of the bipolaron formed by the electron-hole excitations in the presence of Yukawa-type coupling (between nonrelativistic fermions) in three spatial dimension. The electron-hole excitation, which is necessary to the formation of bipolaron, leads to imaginary particle-hole order parameter, and provide finite boson field mass to the single-polaron dispersion in a broken-symmetry phase. We found that the bipolaron exhibits fermi-liquid features as long as the long-range strong interaction is suppressed, and it behave differently compared to the single-polaron. The bosonic momentum determines the mass of boson field propagator and the gap function, and it also related to the self-energies and the single-particle Green's functions. The Thouless criterion is also used during the calculation of gap equation at critical temperature (which become lower in weak-coupling regime), which corresponds to the pole (instability) of the pair propagator in zero center-of-mass freamwork. The mean field term and the bosonic fluctuation-induced contribution to free energy of bipolaron are also studied.