Valley-filling instability and critical magnetic field for interaction-enhanced Zeeman response in doped WSe2 monolayers

Fengyuan Xuan,Su Ying Quek

doi:10.1038/s41524-021-00665-8

Abstract

Carrier-doped transition metal dichalcogenide (TMD) monolayers are of great interest in valleytronics due to the large Zeeman response (g-factors) in these spin-valley-locked materials, arising from many-body interactions. We develop an ab initio approach based on many-body perturbation theory to compute the interaction-enhanced g-factors in carrier-doped materials. We show that the g-factors of doped WSe2 monolayers are enhanced by screened-exchange interactions resulting from magnetic-field-induced changes in band occupancies. Our interaction-enhanced g-factors g* agree well with experiment. Unlike traditional valleytronic materials such as silicon, the enhancement in g-factor vanishes beyond a critical magnetic field Bc achievable in standard laboratories. We identify ranges of g* for which this change in g-factor at Bc leads to a valley-filling instability and Landau level alignment, which is important for the study of quantum phase transitions in doped TMDs. We further demonstrate how to tune the g-factors and optimize the valley-polarization for the valley Hall effect.

Highlights

Valleytronics, the control and manipulation of the valley degree of freedom, is being actively considered as the paradigm for information processing
A major impetus for the renaissance of valleytronics is the recent discovery that H-phase transition metal dichalcogenide (TMD) semiconductor monolayers (MLs) are excellent candidates for valleytronics applications[3,4]
We further identify the values of gÃenh and corresponding ranges of B that lead to a valley-filling instability and expected LL alignment, which are of interest for the investigation of quantum phase transitions in doped TMDs29–34

Summary

Introduction

Valleytronics, the control and manipulation of the valley degree of freedom (valley pseudospin), is being actively considered as the paradigm for information processing. When an external magnetic field is applied normally to the TMD ML, the energies of the valleys shift in equal magnitude and opposite directions. This Zeeman effect is quantified by the orbital and spin magnetic moments, which contribute to the Landé g-factors. In TMD MLs, the intrinsic Landé g-factors are about six times larger[6,7,8,10] than that in silicon, where only the spin magnetic moment dominates[21,22]. We approximate the dielectric screening from a substrate using εmed = (1 + εsub)/253, where εsub is the dielectric constant of the substrate A plane-wave basis: we approximate the effect of screening by a dielectric medium by modifying the static dielectric matrix as follows: εGG0 ðq; 0Þ 1⁄4 εWGGSe0 2 þ ðεmed À 1ÞδGG0 : (21)

Methods

Results

Conclusion