Polaritonic and Excitonic Time Crystals based on TMDC strips in an external periodic potential

TL;DR

This paper demonstrates the existence of time crystal phases in Bose-Einstein condensates of exciton-polaritons and excitons in TMDC nanoribbons under external periodic potentials, confirmed through quantum and stochastic modeling.

Contribution

It introduces the concept of polaritonic and excitonic time crystals in TMDC systems and shows their robustness beyond mean-field approximations.

Findings

Time crystal phases observed in TMDC-based BECs.

Non-trivial oscillating two-point correlators in density profiles.

Time crystal phases persist with quantum corrections.

Abstract

We investigated the dynamics of Bose-Einstein condensates (BECs) under an external periodic potential. We consider two such systems, the first being made of exciton-polaritons in a nanoribbon of transition metal dichalcogenides (TMDCs), such as MoSe$_2$, embedded in a microcavity with a special curvature, which serves as the source of the external potential. The second, made of bare excitons in a nanoribbon of twisted TMDC bilayer, which naturally creates a periodic Moir\'e potential that can be controlled by the angle of twist. We proved that such systems exhibit a Time Crystal (TC) phase. This was demonstrated by the fact that the calculated BEC spatial density profile shows a non-trivial two-point correlator that oscillates in time. These BECs density profiles were calculated by solving the quantum Lindblad master equations for the density matrix within the mean-field approximation. We then go beyond the usual mean-field approach, by adding a stochastic term to the master equation, which corresponds to quantum corrections, and we show that the TC phase is still present.