Coherent Interaction of 2s and 1s Exciton States in Transition-Metal Dichalcogenide Monolayers

TL;DR

This study investigates the coherent interaction between 2s and 1s exciton states in transition-metal dichalcogenide monolayers using femtosecond spectroscopy, revealing exciton interactions and a bound biexciton state.

Contribution

It provides the first experimental evidence of a 2s-1s biexciton bound state and quantifies exciton interaction strengths in WSe2 and MoSe2 monolayers.

Findings

Measured blueshift indicating repulsive 2s-1s exciton interaction

Quantified 2s-1s interaction strength comparable to 1s-1s

Demonstrated existence of 2s-1s biexciton bound state and determined its binding energy

Abstract

We use femtosecond pump-probe spectroscopy to study the coherent interaction of excited exciton states in WSe2 and MoSe2 monolayers via the optical Stark effect. For co-circularly polarized pump and probe, we measure a blueshift which points to a repulsive interaction between the 2s and 1s exciton states. The determined 2s-1s interaction strength is on par with that of the 1s-1s, in agreement with the semiconductor Bloch equations. Furthermore, we demonstrate the existence of a 2s-1s biexciton bound state in the cross-circular configuration in both materials and determine their binding energy.