Crystal valley Hall effect

TL;DR

This paper demonstrates the realization of valley Hall effect without time-reversal symmetry in two-dimensional altermagnetic materials, revealing new topological phases and effects driven by crystal symmetry and strain.

Contribution

It introduces the concept of crystal valley Hall effect in altermagnetic materials and explores strain-induced phase transitions to topological Weyl semimetals.

Findings

Valley Hall effect without time-reversal symmetry in Fe2WSe4 and Fe2WS4

Strain-induced piezomagnetic effect in these materials

Transition to Weyl semimetal phase under biaxial compression

Abstract

The time-reversal symmetry is thought to be a necessary condition for realizing valley Hall effect. If the time-reversal symmetry is broken, whether the valley Hall effect can be realized has not been explored. In this letter, based on symmetry analysis and the first-principles electronic structure calculations, we demonstrate that the vally Hall effect without time-reversal symmetry can be realized in two-dimensional altermagnetic materials Fe$_2$WSe$_4$ and Fe$_2$WS$_4$. Due to crystal symmetry required, the vally Hall effect without time-reversal symmetry is called crystal vally Hall effect. In addition, under uniaxial strain, both monolayer Fe$_2$WSe$_4$ and Fe$_2$WS$_4$ can realize piezomagnetic effect. Under biaxial compressive stress, both monolayer Fe$_2$WSe$_4$ and Fe$_2$WS$_4$ will transform from altermagnetic semiconductor phase to bipolarized topological Weyl semimetal phase. Our work not only provides a new direction for exploring the novel valley Hall effect, but also provides a good platform for exploring altermagnetic semiconductors and altermagnetic topological phase transitions.