Tuning excitons and superfluidity of dipolar excitons in the double layers of kagome lattice by applying circularly polarized irradiation

TL;DR

This paper investigates how circularly polarized light can tune excitonic properties and induce superfluidity in kagome lattice double layers, revealing phase transitions and potential for Bose-Einstein condensation.

Contribution

It introduces a method to control excitonic phases and superfluidity in kagome lattices using circularly polarized irradiation, including predictions of phase transitions and superfluid behavior.

Findings

Circularly polarized light opens a band gap near Dirac points.

Irradiation can induce a transition from semiconducting to excitonic insulating phase.

Superfluidity and Bose-Einstein condensation of dipolar excitons can be observed under irradiation.

Abstract

We present detailed calculations for several significant properties of the kagome lattice. We employ the Floquet-Magnus perturbation expansion to obtain the energy bands and the corresponding wave functions near the Dirac points for the kagome lattice in the presence of circularly or linearly polarized irradiation. In contrast with linearly polarized irradiation, a band gap is opened up near the Dirac points, between the valence and conduction bands in the presence of circularly polarized irradiation. We calculated the exciton binding energy, and the exciton energy for gapped kagome lattice as a function of the frequency and intensity of the irradiation. We compare the exciton binding energy and exciton energy in a monolayer with those in a double layer separated by an insulator to inhibit recombination. We predict that a phase transition in the kagome lattice from the semiconducting phase to the excitonic insulating phase can be induced by applying irradiation. We also examined the conditions for such a phase transition. We explore opportunities to tune exciton binding energy, the energy spectrum of collective excitations, the sound velocity and the critical temperature of the superfluidity by applying circularly polarized irradiation. We propose observation of Bose-Einstein condensation and superfluidity of quasi-two-dimensional dipolar excitons in two-layer kagome lattices in the presence of pumping by circularly polarized light. We have also analyzed the dependence of superfluid density $n_s$ and the temperature of the Kosterlitz-Thouless phase transition temperature on excitonic density n, the interlayer separation D and the parameters for circularly polarized light.