Electrically tunable polarizer based on 2D orthorhombic ferrovalley materials

Abstract

The concept of ferrovalley materials has been proposed very recently. The existence of spontaneous valley polarization, resulting from ferromagnetism, in such hexagonal two-dimensional materials makes nonvolatile valleytronic applications realizable. Here, we introduce a new member of ferrovalley family with orthorhombic lattice, i.e. monolayer group-IV monochalcogenides (GIVMs), in which the intrinsic valley polarization originates from ferroelectricity, instead of ferromagnetism. Combining the group theory analysis and first-principles calculations, we demonstrate that, different from the valley-selective circular dichroism in hexagonal lattice, linearly polarized optical selectivity for valleys exists in the new type of ferrovalley materials. On account of the distinctive property, a prototype of electrically tunable polarizer is realized. In the ferrovalley-based polarizer, a laser beam can be optionally polarized in x-or y-direction, depending on the ferrovalley state controlled by external electric fields. Such a device can be further optimized to emit circularly polarized radiation with specific chirality and to realize the tunability for operating wavelength. Therefore, we show that two-dimensional orthorhombic ferrovalley materials are the promising candidates to provide an advantageous platform to realize the polarizer driven by electric means, which is of great importance in extending the practical applications of valleytronics.

Recent Progress in Two‐Dimensional Ferroelectric Materials

“…Additionally, ferrovalley materials with spontaneous valley polarization have also been recently proposed in 2D ferroelectrics. As a new member of the ferroic family, ferrovalley materials originated from at least two orders, including ferromagnetism [78] and ferroelectricity, [79] show the potential to break through the restriction of the external fields, becoming a new frontier for next-generation nonvolatile information storage.…”

“…As shown in Figure 18a, the occurrence of a reduced symmetry of the valley shown in the band structure of the ferroelectric phase GeSe monolayer implies that the spontaneous valley polarization is induced by 2D IP ferroelectricity. [197] Additionally, Figure 16. Switching of ferroelectric polarization in a) graphene-BTO-SRO (Reproduced with permission.…”

“…Reproduced with permission. [197] Copyright 2017, IOP Publishing Ltd. b) Rashba splitting bands with positive and negative ferroelectric displacements, respectively. Reproduced with permission.…”

Niobium oxide dihalides NbOX2: a new family of two-dimensional van der Waals layered materials with intrinsic ferroelectricity and antiferroelectricity

“…The coupling between FE ordering and the electronic and optical properties of 2D materials can lead to interesting phenomena, such as the bulk photovoltaic 9,38 and ferrovalley effects. 12,39 We will investigate the electronic structures and optical absorption properties for the FE phases in bulk and monolayer NbOX 2 . Fig.…”

“…5(a) with photon energy of 3.15 eV is incident on FE NbOI 2 monolayer, optical absorption along the nonpolar a axis is significantly larger than that along the polar axis, leading to a nearly linearly polarized optical absorption selectivity in NbOI 2 monolayer. 39…”