Evidence for Exciton Crystals in a 2D Semiconductor Heterotrilayer

TL;DR

This paper provides spectroscopic evidence for exciton crystal formation in a 2D WSe2/MoSe2/WSe2 heterotrilayer, revealing novel quantum phases and transitions driven by Coulomb interactions and exciton density.

Contribution

It demonstrates the existence of ordered interlayer exciton crystals in a trilayer, advancing understanding of exciton ordering and phase transitions in 2D heterostructures.

Findings

Evidence for interlayer exciton crystals in trilayer

Observation of exciton density-dependent phase transitions

Detection of exciton crystal to gas and plasma transitions

Abstract

Two-dimensional (2D) transition metal dichalcogenides (TMDC) and their moir\'e interfaces have been demonstrated for correlated electron states, including Mott insulators and electron/hole crystals commensurate with moir\'e superlattices. Here we present spectroscopic evidences for ordered bosons - interlayer exciton crystals in a WSe2/MoSe2/WSe2 trilayer, where the enhanced Coulomb interactions over those in heterobilayers have been predicted to result in exciton ordering. While the dipolar interlayer excitons in the heterobilayer may be ordered by the periodic moir\'e traps, their mutual repulsion results in de-trapping at exciton density n_ex larger than 10^11 cm^-2 to form mobile exciton gases and further to electron-hole plasmas, both accompanied by broadening in photoluminescence (PL) peaks and large increases in mobility. In contrast, ordered interlayer excitons in the trilayer are characterized by negligible mobility and by sharper PL peaks persisting to n_ex approximately 10^12 cm^-2. We present evidences for the predicted quadrupolar exciton crystal and its transitions to dipolar excitons either with increasing n_ex or by an applied electric field. These ordered interlayer excitons may serve as models for the exploration of quantum phase transitions and quantum coherent phenomena.