Electron-Exciton Coupling in 1T-TiSe₂ Bilayer

Abstract

The excitons in solid state are bosons generated by the electron-hole pairs as the Coulomb screening is sufficiently reduced. The exciton condensation can result in exotic physics such as super-fluidity and insulating state. 1T-TiSe2, in the charge density wave (CDW) state, is one of the candidates that may host the exciton condensation. However, to envision its excitonic effect, particularly at the two dimensional limit, that is applicable to future devices, is still challenging. In this study, we realized the epitaxial 1T-TiSe2 bilayer, the two dimensional (2D) limit for its 2×2×2 CDW order, to explore the exciton-associated effect. By means of high-resolution scanning tunneling spectroscopy and quasiparticle interference, we discovered an unexpected state residing below the conduction band and right within the CDW gap region. As corroborated by our theoretical analysis, this mysterious phenomenon is in good agreement with the electron-exciton coupling. Our study provides a material platform to explore the exciton-based electronics and opto-electronics.

Manipulation of band gap in 1T-TiSe2 via rubidium deposition

“…It has also been proposed that the broad feature is induced by the strong electron-exciton coupling effect in 1T -TiSe 2 . [22] -0.2 0.2 As shown in Figs. 2(c) and 2(d), in comparison with bands in the normal state, the valence bands are nearly unchanged at the A point, but reconstruct significantly at the Γ point.…”