Symmetry-dependent antiferromagnetic proximity effects on valley splitting

TL;DR

This paper investigates how antiferromagnetic proximity effects influence valley splitting in transition-metal dichalcogenide monolayers, revealing symmetry protections and expanding possibilities for valley degree manipulation.

Contribution

It introduces an extended three-band model and first-principles calculations to systematically study AFM proximity effects on valley degeneracy, which was previously unexplored.

Findings

AFM proximity can break valley degeneracy under certain symmetries

Symmetries like 'time-reversal + fractional translation' or 'mirror' protect valley degeneracy

The extended TB model accurately describes valley physics with complex magnetic proximity effects

Abstract

Various physical phenomena have been discovered by tuning degrees of freedom, among which there is the degree of freedom (DOF) -- "valley". The typical valley materials are characterized by two degenerate valley states protected by time-reversal symmetry (TS). These states indexed by valley DOF have been measured and manipulated for emergent valley-contrasting physics with the broken valley degeneracy. To achieve the valley splitting resulted from TS breaking, previous studies mainly focused on magnetic proximity effect provided by ferromagnetic (FM) layer. Nevertheless, the anti-ferromagnetic (AFM) proximity effect on the valley degeneracy has never been investigated systematically. In this work, we construct the composites consisting of a transitionmetal dichalcogenide (TMD) monolayer and a proximity layer with specific intra-plane AFM configurations. We extend the three-band model to describe the valley states of such systems. It is shown that either "time-reversal + fractional translation" or "mirror" symmetry has been proved to protect valley degeneracy. Additionally, first-principles calculations based on density functional theory (DFT) have been performed to verify the results obtained from the extended tight-binding (TB) model. The TB method introduced in the present work can properly describe the low-energy physics of valley materials that couple to the proximity with complex magnetic configurations. The results expand the range of qualified proximity layers for valley splitting, enabling more flexible manipulation of valley degree.