The superfluid phase transition in two-dimensional excitonic systems

TL;DR

This paper investigates the superfluid phase transition in two-dimensional excitonic systems, demonstrating the role of excitonic insulator states and phase stiffness in enabling BKT superfluidity at low temperatures.

Contribution

It introduces a theoretical analysis of the superfluid transition in 2D excitonic systems using the extended Falicov-Kimball model, highlighting the importance of excitonic insulator phases.

Findings

Existence of excitonic insulator phase in 2D systems.

Particle phase stiffness leads to BKT superfluid state.

Excitonic insulator phase is essential for quasi-long-range order.

Abstract

We study the superfluid phase transition in the two-dimensional (2D) excitonic system. Employing the extended Falicov-Kimball model (EFKM) and considering the local quantum correlations in the system composed of conduction band electrons and valence band holes we demonstrate the existence of the excitonic insulator (EI) state in the system. We show that at very low temperatures, the particle phase stiffness in the pure-2D excitonic system, governed by the non-local cross correlations, is responsible for the vortex-antivortex binding phase-field state, known as the Berezinskii-Kosterlitz-Thouless (BKT) superfluid state. We demonstrate that the existence of excitonic insulator phase is a necessary prerequisite, leading to quasi-long-range order in the 2D excitonic system.