Symmetry-forbidden intervalley scattering by atomic defects in monolayer transition-metal dichalcogenides

TL;DR

This paper reveals that certain atomic defects in monolayer transition-metal dichalcogenides can be symmetry-forbidden from causing intervalley scattering, offering a new protection mechanism for their valley properties.

Contribution

It introduces a defect-dependent symmetry selection rule that prevents intervalley scattering, supported by theoretical predictions and potential experimental verification via FT-STS.

Findings

Symmetry of atomic defects can forbid intervalley scattering.

Fourier transform scanning tunneling spectroscopy can identify defect types.

Recent experiments' absence of FT-STS peaks is explained by this symmetry protection.

Abstract

Intervalley scattering by atomic defects in monolayer transition metal dichalcogenides (TDMs; MX2) presents a serious obstacle for applications exploiting their unique valley-contrasting properties. Here, we show that the symmetry of the atomic defects can give rise to an unconventional protection mechanism against intervalley scattering in monolayer TMDs. The predicted defect-dependent selection rules for intervalley scattering can be verified via Fourier transform scanning tunneling spectroscopy (FT-STS), and provide a unique identification of, e.g., atomic vacancy defects (M vs X). Our findings put the absence of the intervalley FT-STS peak in recent experiments in a different perspective.