Coexisting Triferroic and Multiple Types of Valley Polarization by Structural Phase Transition in Two-Dimensional Materials

TL;DR

This paper proposes a mechanism to achieve coexistence of triferroic order and multiple valley polarizations in 2D materials through structural phase transitions, enabling advanced spintronic and valleytronic device functionalities.

Contribution

It introduces a novel approach to realize multiferroic and valley-polarized states in 2D materials via phase transitions and interlayer manipulation.

Findings

1T and 2H phase OsBr2 monolayers exhibit distinct valley polarization properties.

Bilayer OsBr2 shows tri-state valley polarization due to symmetry breaking.

Valley and ferroelectric polarizations can be controlled by interlayer sliding and phase transitions.

Abstract

The multiferroic materials, which coexist magnetism, ferroelectric, and ferrovalley, have broad practical application prospects in promoting the miniaturization and integration of spintronic and valleytronic devices. However, it is rare that there are triferroic orders and multiple types of valley polarization in a real material. Here, we propose a mechanism to realize triferroic order coexistence and multiple types of valley polarization by structural phase transition in two-dimensional (2D) materials. The 1T and 2H phase OsBr2 monolayers exhibit non-magnetic semiconductor and ferromagnetic semiconductor with valley polarization up to 175.49 meV, respectively. Interestingly, the 1T phase OsBr2 bilayer shows the tri-state valley polarization due to lattice symmetry breaking, while the valley polarization of 2H phase bilayer originates from the combined effect of time-reversal symmetry breaking and spin-orbit coupling. Furthermore, the valley polarization and ferroelectric polarization of 1T phase AB stackings and 2H phase AA stackings can be manipulated via interlayer sliding. Importantly, we have verified that the 2H phase can be transformed to 1T phase by Li+ ion intercalation, while the 2H phase can occur the structural phase transition into the 1T phase by infrared laser induction. Our work provides a feasible strategy for manipulating valley polarization and a design idea for nano-devices with nonvolatile multiferroic properties.