A Molecular Perspective of Exciton Condensation from Particle-hole Reduced Density Matrices

TL;DR

This paper reviews the theoretical and experimental progress in understanding exciton condensation, emphasizing a molecular approach that links it to broader quantum phenomena and potential technological applications.

Contribution

It introduces a molecular perspective on exciton condensation using particle-hole reduced density matrices, connecting theory with experiments and related quantum phenomena.

Findings

Eigenvalue greater than one indicates exciton condensation

Framework links exciton condensation to Bose-Einstein condensation and superconductivity

Molecular approach integrates exciton phenomena with quantum materials

Abstract

Exciton condensation, the Bose-Einstein-like condensation of quasibosonic particle-hole pairs, has been the subject of much theoretical and experimental interest and holds promise for ultra-energy-efficient technologies. Recent advances in bilayer systems, such as transition metal dichalcogenide heterostructures, have brought us closer to the experimental realization of exciton condensation without the need for high magnetic fields. In this perspective, we explore progress towards understanding and realizing exciton condensation, with a particular focus on the characteristic theoretical signature of exciton condensation: an eigenvalue greater than one in the particle-hole reduced density matrix, which signifies off-diagonal long-range order. This metric bridges the gap between theoretical predictions and experimental realizations by providing a unifying framework that connects exciton condensation to related phenomena, such as Bose-Einstein condensation and superconductivity. Furthermore, our molecular approach integrates exciton condensation with broader excitonic phenomena, including exciton-related entanglement and correlation, unlocking potential advancements in fields like quantum materials and energy transport. We discuss connections between recent experimental and theoretical work and highlight the discoveries that may arise from approaching exciton condensation from a molecular perspective.