Proposal for valleytronic materials: ferrovalley metal and valley gapless semiconductor

TL;DR

This paper introduces the concepts of ferrovalley metal and valley gapless semiconductor in bilayer systems, demonstrating how electric fields can tune valley properties, confirmed by first-principles calculations on bilayer RuBr2.

Contribution

It proposes new valleytronic phases and demonstrates electric-field tuning of valley splitting and polarization in bilayer materials, supported by first-principles calculations.

Findings

FVM and VGS can be realized in bilayer RuBr2 with electric field.

Electric field enhances valley splitting and reverses valley polarization.

Out-of-plane magnetization and large valley splitting are key for tuning.

Abstract

Valleytronic materials can provide new degrees of freedom to future electronic devices. In this work, the concepts of the ferrovalley metal (FVM) and valley gapless semiconductor (VGS) are proposed, which can be achieved in valleytronic bilayer systems by electric-field tuning, where the interaction between out-of-plane ferroelectricity and A-type antiferromagnetism can induce layer-polarized anomalous valley Hall (LP-AVH) effect. The K and -K valleys of FVM are both metallic, and electron and hole carriers simultaneously exist. In the extreme case, the FVM can become VGS by analogizing spin gapless semiconductor (SGS). Moreover, it is proposed that the valley splitting enhancement and valley polarization reversal can be achieved by electric field in valleytronic bilayer systems. Taking the bilayer $\mathrm{RuBr_2}$ as an example, our proposal is confirmed by the first-principle calculations. The FVM and VGS can be achieved in bilayer $\mathrm{RuBr_2}$ by applying electric field. With appropriate electric field range, increasing electric field can enhance valley splitting, and the valley polarization can be reversed by flipping electric field direction. To effectively tune valley properties by electric field in bilayer systems, the parent monolayer should possess out-of-plane magnetization, and have large valley splitting. Our results shed light on the possible role of electric field in tuning valleytronic bilayer systems, and provide a way to design the ferrovalley-related material by electric field.