Single layer TlX (X=Cl/Br/I) with ferroelectric-valley coupling potential for electrically tunable polarizer

Abstract

The ferrovalley materials are generally the hexagonal lattice systems with ferromagnetism-valley coupling, in which the intrinsic ferromagnetism can induce valley polarization. However, as of now the number of found ferrovalley materials is still limited. In this article, the TlX (X=Cl/Br/I) single-layer (SL) are proposed with a tetragonal lattice structure as well as ferroelectricity-valley coupling. And they possess good mechanical and dynamic stability, which is expected to be synthesized in experiments. When applying in-plane electric field or uniaxial strain, the SL-TlX (X=Cl/Br/I) show robust valley polarization. Because the direction of polarization of SL-TlX (X=Cl/Br/I) can be controlled with rapid reversal of electric field direction, the SL-TlX (X=Cl/Br/I) are the potential valleytronic materials with electrically controllable valley polarization. The SL-TlX (X=Cl/Br/I) have linear optical selection rules, different from the traditional hexagonal lattice systems, making them potential for manufacturing the electrically controllable optical filters.