Valley-dependent Exciton Fine Structure and Autler-Townes Doublets from Berry Phases in Monolayer Molybdenum Diselenide

TL;DR

This paper demonstrates the observation and control of Berry-phase induced splitting of exciton states in monolayer MoSe2, revealing valley-dependent effects and Autler-Townes doublets, advancing quantum manipulation in 2D semiconductors.

Contribution

It reports the first experimental observation of Berry-phase effects on exciton states and their control via intraexciton optical Stark spectroscopy in monolayer MoSe2.

Findings

Berry-phase induced splitting of 2p exciton states observed

Valley-dependent Autler-Townes doublets demonstrated

Energy difference of ±14 meV between exciton states in different valleys

Abstract

The Berry phase of Bloch states can have profound effects on electron dynamics lead to novel transport phenomena, such as the anomalous Hall effect and the valley Hall effect. Recently, it was predicted that the Berry phase effect can also modify the exciton states in transition metal dichalcogenide monolayers, and lift the energy degeneracy of exciton states with opposite angular momentum through an effective valley-orbital coupling. Here, we report the first observation and control of the Berry-phase induced splitting of the 2p-exciton states in monolayer molybdenum diselenide using the intraexciton optical Stark spectroscopy. We observe the time-reversal-symmetric analog of the orbital Zeeman effect resulting from the valley-dependent Berry phase, which leads to energy difference of +14 (-14) meV between the $2p^+$ and $2p^-$ exciton states in +K (-K) valley, consistent with the ordering from our ab initio GW-BSE results. In addition, we show that the light-matter coupling between intraexciton states are remarkably strong, leading to prominent valley-dependent Autler-Townes doublet under resonant driving. Our study opens up new pathways to coherently manipulate the quantum states and excitonic excitation with infrared radiation in two-dimensional semiconductors.