Spontaneous Valley Polarization in a Ferromagnetic Fe(OH)₂ Monolayer

Abstract

At present, creating sizable spontaneous valley polarization is at the center of the study of valleytronics, which, however, is still a huge challenge. In this work, we determined that the ferromagnetic Fe(OH) 2 monolayer of the hexagonal lattice is a highly appealing candidate for valleytronics by using first-principles calculations in conjunction with tight-binding model analysis. In light of the simultaneous inversion symmetry breaking and time-reversal symmetry breaking, we illustrated that the strong spin−orbit coupling and robust ferromagnetic exchange interaction cause a spontaneous valley polarization as large as 67 meV for Fe(OH) 2 , indicative of room-temperature application. In addition, the physics of valley-selective circular dichroism, spin/valley Hall effects, and topological phase transition were also discussed.

Piezoelectricity and valley polarization in a semilithiated 2H-TiTe2 monolayer with near room-temperature ferromagnetism

“…The basis functions of the conduction band made up of the Ti-e 1 (3d xy , 3d x 2 -y 2) orbitals will result in an energy difference with a magnitude of 4a between the ÀK and +K valleys, whereas the basis functions of the valence band consisting of the Ti-a (3d z 2) orbital in no difference in energy of two valleys. 18,21 These results are well consistent with the valley polarization in Li@2H-TiTe 2 obtained from firstprinciples calculations. Alternatively, it has been well-known that in the NM 2H-TMDCs, valley polarization can be realized by valley-selective circular dichroism.…”

“…Therefore, the energy degeneracy between the − K and + K valleys is removed so that the valley polarized state is realized in the conduction band of Li@2H-TiTe 2 rather than in the frequently reported valence band of other ferrovalley materials. Remarkably, the valley polarization with a fully clean energy window reaches as sizable as 160 meV, which is larger than or comparable to that reported in monolayers VSe 2 (78.2 meV), 11 FeClBr (188 meV), 14 LaH 2 (137 meV), 15 Cr 2 COF MXene (291/379 meV), 16 CeI 2 (208 meV), 17 2H-RuCl 2 (240 meV), 18 CrHfN 2 Cl 2 (55 meV), 19 RuClX (X = F, Br) (194/226 meV), 20 Fe(OH) 2 (67 meV), 21 VSSe (85 meV), 29 and VClBr (70 meV). 30 It is noteworthy that the valley polarization of the conduction band will be reversed when the magnetization points to the − z direction, as shown in Fig.…”

“…Up to date, 2D ferrovalley semiconductors with the clean valley states and considerable valley polarization for room-temperature operation are extremely rare and yet to be verified experimentally. [14][15][16][17][18][19][20][21] It is therefore meaningful to accelerate the discovery of such ferrovalley materials for designing valley-based electronic and optoelectronic devices.…”

Insight into the quantum anomalous Hall states in two-dimensional kagome Cr3Se4 and Fe3S4 monolayers

“…Such sizable gaps are larger than many proposed systems, which make them potential candidates for application in spintronic devices. To further explain the large band gaps induced by SOC in both systems, the Hamiltonian of SOC with the same spin states can be written as 71,72 represents the orbital angular momentum and Ŝ stands for the spin angular momentum. In addition, θ and φ are the azimuth angle and polar angle, respectively.…”

“…Such sizable gaps are larger than many proposed systems, which make them potential candidates for application in spintronic devices. To further explain the large band gaps induced by SOC in both systems, the Hamiltonian of SOC with the same spin states can be written as 71,72 H ð0Þ…”