Valley polarization in twisted altermagnetism

TL;DR

This paper proposes a method to achieve valley polarization in twisted altermagnetic materials by applying an out-of-plane electric field, enabling new functionalities in spintronics and valleytronics.

Contribution

It introduces a novel approach to induce valley polarization in twisted altermagnets through electric fields, supported by theoretical models and first-principles calculations.

Findings

Electric field induces valley polarization in twisted altermagnets.

Electric field can also create valley/spin-gapless semiconductors and half metals.

Verification possible in twisted bilayer VOBr and monolayer Ca(CoN)2.

Abstract

The combination of altermagnetism, twistronics and valleytronics is of great significance for potential applications in advanced electronic devices. Twisted magnetic van der Waals bilayers have been identified as an ideal platform for altermagnetism of any type, such as $d$-wave, $g$-wave, and $i$-wave, by choosing the constituent monolayer with specific symmetry [arXiv:2404.17146 (2024)]. Here, we propose a way for achieving valley polarization in twisted altermagnetism by applying out-of-plane external electric field. Since the out-of-plane electric field creates a layer-dependent electrostatic potential, the valleys form different layers will stagger, producing valley polarization. We also demonstrate the effectiveness of our proposed way using the twisted tight-binding model. It is found that the applied electric field can also induce valley/spin-gapless semiconductor and half metal besides valley polarization. Based on first-principles calculations, our proposed way to achieve valley polarization can be verified in twisted bilayer VOBr and monolayer $\mathrm{Ca(CoN)_2}$ as a special twisted altermagnet. These findings provide new opportunities for innovative spintronics, twistronics and valleytronics applications.