Sign-reversible valley-dependent Berry phase effects in 2D valley-half-semiconductors

Xiaodong Zhou,Zeying Zhang,Yugui Yao,Yuriy Mokrousov,Run-Wu Zhang,Wanxiang Feng

doi:10.1038/s41524-021-00632-3

Abstract

Manipulating valley-dependent Berry phase effects provides remarkable opportunities for both fundamental research and practical applications. Here, by referring to effective model analysis, we propose a general scheme for realizing topological magneto-valley phase transitions. More importantly, by using valley-half-semiconducting VSi2N4 as an outstanding example, we investigate sign change of valley-dependent Berry phase effects which drive the change-in-sign valley anomalous transport characteristics via external means such as biaxial strain, electric field, and correlation effects. As a result, this gives rise to quantized versions of valley anomalous transport phenomena. Our findings not only uncover a general framework to control valley degree of freedom, but also motivate further research in the direction of multifunctional quantum devices in valleytronics and spintronics.

Highlights

Recent advances in valleytronics are mainly based on the paradigm of time-reversal-connected valleys, which generates valley polarization by an external field, dynamically or statically[1,2,3]
For achieving widespread applications of valleytronics, intrinsic properties are to be prioritized higher than external tunability
The proposal of twodimensional (2D) ferrovalley materials has laid out a magnetovalleytronics composite paradigm based on spontaneous valley polarization induced by the integrated effects of magnetic order and spin-orbit coupling (SOC), which can radically reduce additional costs of the applied external fields[4]

Summary

INTRODUCTION

Recent advances in valleytronics are mainly based on the paradigm of time-reversal-connected valleys, which generates valley polarization by an external field, dynamically or statically[1,2,3]. Intrinsic valleytronics materials hosting spontaneous valley polarization are most desirable, owing to their advantages of robustness, power efficiency, and simplicity in operation In this regard, alternatives to the existing paradigms are intensively sought after. When valley couples with intrinsic ferromagnetic order, the valleydependent Berry phase effects can generate emergent valley anomalous transport phenomena − e.g., valley Hall effect[5,6,7,8,9,10,11] and valley Nernst effect12,13) − making it possible to realize highperformance quantum devices and raising an intensive interest in materials systems which host magneto-valley traits. We find that topological phase transitions with magneto-valley coupling can exhibit valleydependent Berry phase effects which manifest in prominent valley sign-reversible anomalous transport fingerprints

RESULTS AND DISCUSSION

Zhou et al 2

METHODS