Valley-controlled many-body exciton interactions in monolayer WSe$_2$ phototransistors

TL;DR

This study demonstrates all-optical, valley-selective control of many-body exciton interactions in monolayer WSe$_2$, revealing nonlinear effects and valley-dependent responses crucial for valleytronics and excitonic applications.

Contribution

It introduces a novel all-optical method to control many-body exciton interactions via valley-selective excitation in monolayer WSe$_2$, expanding the toolkit beyond electrical gating.

Findings

Circular excitation induces valley-dependent exciton renormalization.

Two-fold enhancement of sublinear photocurrent scaling under circular excitation.

Microscopic model reproduces nonlinear valley-selective response.

Abstract

Many-body exciton interactions shape the optoelectronic response of atomically-thin transition metal dichalcogenides, yet optical control of these interactions remains largely unexplored. To date, modulation of exciton-exciton interactions has primarily relied on electrical gating or van der Waals engineering. Here, we demonstrate all-optical control of many-body exciton interactions in monolayer WSe$_2$ via valley-selective excitation using polarization-resolved pulsed-laser photocurrent spectroscopy. Circular excitation selectively populates excitons in a single valley, whereas linear excitation populates both valleys, inducing a valley-dependent nonlinear photoresponse. We observe helicity-dependent exciton renormalization, alongside a two-fold enhancement of sublinear photocurrent scaling under circular excitation, reflecting single-valley population of interacting excitons. A microscopic model incorporating intervalley-exchange and exciton-exciton annihilation mediated by dark and bright exciton populations reproduces the nonlinear valley-selective response. These results establish the valley degree of freedom as an all-optical control parameter for tuning many-body excitonic effects and, exploring correlated exciton states and valleytronic applications in two-dimensional semiconductors.