A possible electronic state quasi-half-valley-metal in $\mathrm{VGe_2P_4}$ monolayer

TL;DR

This paper proposes the concept of quasi-half-valley-metal (QHVM) in 2D materials, exemplified by VGe2P4 monolayer, which exhibits spontaneous valley polarization and tunable valley properties under electric fields, advancing valleytronics applications.

Contribution

It introduces the novel QHVM concept, demonstrating its realization in VGe2P4 monolayer through first-principles calculations and electric field tuning.

Findings

VGe2P4 monolayer is ferromagnetic with out-of-plane magnetization.

QHVM state can be maintained and tuned by electric fields.

Intrinsic spontaneous valley polarization is confirmed in VGe2P4.

Abstract

One of the key problems in valleytronics is to realize valley polarization. Ferrovalley (FV) semiconductor and half-valley-metal (HVM) have been proposed, which possess intrinsic spontaneous valley polarization. Here, we propose the concept of quasi-half-valley-metal (QHVM), including electron and hole carriers with only a type of carriers being valley polarized. The QHVM may realize separation function of electron and hole. A concrete example of $\mathrm{VGe_2P_4}$ monolayer is used to illustrate our proposal through the first-principle calculations. To better realize QHVM, the electric field is applied to tune related valley properties of $\mathrm{VGe_2P_4}$. Within considered electric field range, $\mathrm{VGe_2P_4}$ is always ferromagnetic (FM) ground state, which possesses out-of-plane magnetization by calculating magnetic anisotropy energy (MAE) including magnetic shape anisotropy (MSA) and magnetocrystalline anisotropy (MCA) energies. These out-of-plane FM properties guarantee intrinsic spontaneous valley polarization in $\mathrm{VGe_2P_4}$. Within a certain range of electric field, the QHVM can be maintained, and the related polarization properties can be effectively tuned. Our works pave the way toward two-dimensional (2D) functional materials design of valleytronics.