Observation of quasi-steady dark excitons and gap phase in a doped semiconductor

TL;DR

This study demonstrates the creation, detection, and control of dark excitons in a doped semiconductor using angle-resolved photoemission spectroscopy, revealing an excitonic gap phase under quasi-equilibrium conditions.

Contribution

It introduces a novel method to observe and manipulate dark excitons and the excitonic gap phase in a doped semiconductor under quasi-equilibrium conditions.

Findings

Detection of dark excitons in a doped semiconductor.

Observation of an anisotropic excitonic gap phase.

Extension of dark exciton studies to quasi-equilibrium states.

Abstract

Exciton plays an important role in optics and optics-related behaviors and leads to novel correlated phases like charge order, exciton insulator, and exciton-polariton condensation. Dark exciton shows distinct properties from bright one. However, it cannot be directly detected by conventional optic measurements. The electronic modulation effect of dark excitons in quasi-equilibrium distribution, critical for electronic devices in working status, is still elusive. Here, using angle-resolved photoemission spectroscopy, we report creating, detecting, and controlling dark excitons in the quasi-equilibrium distribution in a doped semiconductor SnSe2. Surprisingly, we observe an excitonic gap phase, with a conduction band opening an anisotropic gap. Our results broaden the scope of dark excitons, extending their studies from the picosecond timescale in the ultrafast photoemission process to conditions occurring under quasi-equilibrium. We reveal the light-matter interaction in the engineering of electronic structures and provide a new way to realize the excitonic gap phase in semiconductors with large band gaps.