Orbital angular momentum analysis for giant spin splitting in solids and nanostructures

Abstract

Giant spin splitting (GSS) of electronic bands, which is several orders of magnitude greater than the standard Rashba effect has been observed in various systems including noble-metal surfaces and thin films of transition-metal dichalcogenides. Previous studies reported that orbital angular momentum (OAM) is not quenched in some GSS materials and that the atomic spin-orbit interaction (SOI) generates spin splitting in some solid states via the interorbital hopping. Although the unquenched OAM may be closely related to the interorbital hopping, their relationship is hardly studied in the aspect of using the unquenched OAM as a control parameter of GSS. Here, we analyze OAM in GSS materials by using the interorbital-hopping mechanism and first-principles calculations. We report that the interatomic hopping between different-parity orbitals, which is generated by specific broken mirror symmetry, produces k-dependent OAM, resulting in valley-dependent GSS in WSe2 monolayer, Rashba-type GSS in Au (111) surface, and Dresselhaus-type GSS in bulk HgTe. We also demonstrate systematic control of OAM by pressure, external fields, and substrates, thereby controlling the spin splitting, and discuss the temperature dependence of OAM. Our results provide a simplified picture for systematic design and control of GSS materials.

Thickness dependence of work function, ionization energy, and electron affinity of Mo and W dichalcogenides from DFT and GW calculations

“…In the case of bulk, the spin-orbit coupling has relatively small effect compared with 2D layers. Also, the spin splitting in the conduction band is much smaller than that in the valence band because the enhancement of the spin splitting in 2D TMDs is due to the orbital angular momentum generated by the broken mirror symmetry [56]. Thus, for few-layer systems, the giant spin splitting raises the VBM at the K point, resulting in a direct band gap if the CBM is also at the K point.…”

Prediction of a new two-dimensional valleytronic semiconductor MoGe2P4 with large valley spin splitting

“…Due to the existence of non-zero hL Z i, valley spin splitting occurs when considering the strong SOC of Mo. 45,46…”

Enhanced stability of two-dimensional halide perovskites under an electric field for photocatalytic HI splitting

“…39 Therefore, the thermodynamic stability of BMPI with surface-adsorbed H 2 O relative to the intercalated case is of primary importance for photocatalyst applications while the H 2 O migration energy barrier needs to be high as well. To improve the stability, one can consider effective ways of modulating the electronic structure of low-dimensional materials such as applying an external electric eld ( Ẽext ), [43][44][45] chemical doping [46][47][48] as well as encapsulation. [49][50][51][52][53] Several studies have been reported such that the efficiency of catalysts is improved using the external eld by modulating the chemical reactivity 54,55 such as eld-assisted catalysts 56,57 and bipolar electrochemical cells.…”