Multiple mobile excitons manifested as sidebands in quasi-one-dimensional metallic TaSe3

TL;DR

This study uses angle-resolved photoemission spectroscopy to detect and analyze dispersing excitons in quasi-one-dimensional metallic TaSe3, revealing multiple excitonic states and their tunability via surface doping.

Contribution

It provides the first direct observation of dispersing excitons in TaSe3 and demonstrates control over exciton properties through surface doping.

Findings

Detection of dispersing excitons in TaSe3

Identification of intrachain and interchain excitons

Tunable exciton properties via surface doping

Abstract

Charge neutrality and their expected itinerant nature makes excitons potential transmitters of information. However, exciton mobility remains inaccessible to traditional optical experiments that only create and detect excitons with negligible momentum. Here, using angle-resolved photoemission spectroscopy, we detect dispersing excitons in the quasi-one-dimensional metallic trichalcogenide, TaSe3. The low density of conduction electrons and the low dimensionality in TaSe3 combined with a polaronic renormalization of the conduction band and the poorly screened interaction between these polarons and photo-induced valence holes leads to various excitonic bound states that we interpret as intrachain and interchain excitons, and possibly trions. The thresholds for the formation of a photo-hole together with an exciton appear as side valence bands with dispersions nearly parallel to the main valence band, but shifted to lower excitation energies. The energy separation between side and main valence bands can be controlled by surface doping, enabling the tuning of certain exciton properties.