Preformed excitonic liquid route to a charge density wave in 2H-TaSe$_2$

TL;DR

This paper proposes that the charge density wave in 2H-TaSe2 originates from a Bose condensation of preformed excitons, challenging the traditional nested band structure explanation, supported by advanced theoretical calculations.

Contribution

It introduces a strong coupling excitonic liquid framework for understanding charge density waves in 2H-TaSe2, supported by local density approximation and multiorbital dynamical mean-field theory.

Findings

The excitonic liquid scenario aligns with experimental normal state data.

Charge density waves are viewed as instabilities of a preformed excitonic liquid.

Supports a shift from band nesting to strong coupling mechanisms in CDW formation.

Abstract

Recent experiments on 2H-TaSe$_2$ contradict the long-held view of the charge density wave arising from a nested band structure. An intrinsically strong coupling view, involving a charge density wave state arising as a Bose condensation of preformed excitons emerges as an attractive, albeit scantily investigated alternative. Using local density approximation plus multiorbital dynamic mean-field theory, we show that this scenario agrees with a variety of normal state data for 2H-TaSe$_{2}$. Based thereupon, the ordered states in a subset of dichalcogenides should be viewed as instabilities of a correlated, preformed excitonic liquid.