Preformed Excitons, Orbital Selectivity, and Charge-Density-Wave Order in 1T-TiSe_2

TL;DR

This paper proposes that preformed excitonic liquids, characterized by orbital-selective dynamical localization, drive charge-density-wave order in 1T-TiSe2, and these fluctuations may also mediate superconductivity in transition metal dichalcogenides.

Contribution

It introduces a novel excitonic liquid framework supported by advanced electronic structure calculations to explain CDW and superconductivity in 1T-TiSe2.

Findings

Quantitative match with spectral and transport data in normal and CDW phases.

Orbital-selective dynamical localization linked to preformed excitonic liquids.

Soft excitonic fluctuations potentially mediate superconductivity.

Abstract

Traditional routes to Charge-Density-Wave in transition metal dichalcogenides, relying on Fermi surface nesting or Jahn-Teller instabilities have recently been brought into question. While this calls for exploration of alternative views, paucity of theoretical guidance sustains lively controversy on the origin of, and interplay between CDW and superconductive orders in transition metal dichalcogenides. Here, we explore a preformed excitonic liquid route, heavily supplemented by modern correlated electronic structure calculations, to an excitonic-CDW order in 1T-TiSe$_{2}$. We show that orbital-selective dynamical localisation arising from preformed excitonic liquid correlations is somewhat reminiscent to states proposed for $d$- and $f$-band quantum criticality at the border of magnetism. Excellent quantitative explication of a wide range of spectral and transport responses in both normal and CDW phases provides strong support for our scenario, and suggests that soft excitonic liquid fluctuations mediate superconductivity in a broad class of transition metal dichalcogenides on the border of CDW. This brings the transition metal dichalcogenides closer to the bad actors in $d$- and $f$-band systems, where anomalously soft fluctuations of electronic origin are believed to mediate unconventional superconductivity on the border of magnetism.