# Microsecond dark-exciton valley polarization memory in 2D heterostructures

## TL;DR

This paper demonstrates that dark excitons in 2D heterostructures can maintain valley polarization for microseconds, significantly longer than previous excitonic states, due to magnetic field effects.

## Contribution

It reveals that magnetic field induced suppression of valley mixing extends dark exciton valley polarization lifetime to microseconds in 2D heterostructures.

## Key findings

- Dark excitons exhibit microsecond valley polarization lifetime.
- Magnetic field and temperature influence dark exciton lifetime.
- Long-lived dark excitons are promising for quantum applications.

## Abstract

Transition metal dichalcogenides (TMDs) have valley degree of freedom, which features optical selection rule and spin-valley locking, making them promising for valleytronics devices and quantum computation. For either application, a long valley polarization lifetime is crucial. Previous results showed that it is around picosecond in monolayer excitons, nanosecond for electrons, holes or local excitons and tens of nanosecond for interlayer excitons. Here we show that dark excitons in 2D heterostructures provide a microsecond valley polarization memory thanks to the magnetic field induced suppression of valley mixing. The lifetime of the dark excitons shows magnetic field and temperature dependence which is consistent with the theoretical prediction. The long dark exciton lifetime and valley polarization lifetime in 2D heterostructures make them promising for long-distance exciton transport and macroscopic quantum state generations.