# Tuning valley polarization of moiré trapped biexcitons by fine structure occupation in WS2/WSe2 heterostructures

## TL;DR

Researchers found a way to control valley polarization in WS2/WSe2 heterostructures by manipulating biexcitons, achieving up to 55% polarization at 120 K.

## Contribution

The study demonstrates tunable valley polarization in moiré-trapped biexcitons through fine structure occupation.

## Key findings

- Valley polarization of moiré-trapped biexcitons reaches ~55% at 120 K.
- Fine structure splitting of 2.77 meV is observed and matches theoretical predictions.

## Abstract

Two-dimensional transition metal dichalcogenides (TMDs) heterostructures formed moiré superlattices have emerged as a new platform for exploring correlated excitonic states and valleytronic phenomena. Despite the significant progress in moiré-trapped single excitons, the valley polarization and fine structure of moiré-trapped biexcitons remain poorly understood, with the existing studies reporting only limited or zero polarization and lacking insight into the underlying mechanisms. Here, we study the moiré-trapped interlayer biexcitons in WS2/WSe2 heterostructures through power- and temperature-dependent photoluminescence (PL) spectroscopy. We find that the valley polarization of these biexcitons can be effectively tuned, reaching ~\documentclass[12pt]{minimal}
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\begin{document}$$55\%$$\end{document}55% at 120 K. This behavior is attributed to the different occupation of intravalley and intervalley biexcitons within the fine structure, with the intravalley biexcitons playing a dominant role. The power-dependent energy splitting and temperature-dependent polarization trends further confirm the existence of biexciton fine structure and its influence on valley polarization. Furthermore, the experiment revealed a fine structure splitting of 2.77 meV, consistent with theoretical calculations. Our study provides new insight into the rational control of excitonic states in moiré superlattices and establishes a basis for developing advanced valleytronic devices, such as polarization-sensitive photodetectors and quantum light sources.

The authors show that, by tuning the occupation of moiré-trapped interlayer biexcitons in WS2/WSe2 heterostructures, their valley polarization can reach 55% at 120 K, highlighting the potential for valleytronic devices.