We have calculated the longitudinal acoustic phonon limited electron mobility of 14 two-dimensional semiconductors with composition of MX ₂, where M (= Mo, W, Sn, Hf, Zr and Pt) is the transition metal, and X is S, Se and Te. We treated the scattering matrix by the deformation potential approximation. We found that out of 14 compounds, MoTe₂, HfSe₂ and ZrSe₂ are promising regarding to their possible high mobility and finite band gap. The phonon limited mobility can be above 2,500 cm²·V⁻¹·s⁻¹ at room temperature.

Neither of the two typical two-dimensional materials, graphene and single layer MoS ${}_2$ , are good enough for developing semiconductor logical devices. We calculated the electron mobility of 14 two-dimensional semiconductors with composition of MX ${}_2$ , where M (=Mo, W, Sn, Hf, Zr and Pt) are transition metals, and Xs are S, Se and Te. We approximated the electron phonon scattering matrix by deformation potentials, within which long wave longitudinal acoustical and optical phonon scatterings were included. Piezoelectric scattering in the compounds without inversion symmetry is also taken into account. We found that out of the 14 compounds, WS ${}_2$ , PtS ${}_2$ and PtSe ${}_2$ are promising for logical devices regarding the possible high electron mobility and finite band gap. Especially, the phonon limited electron mobility in PtSe ${}_2$ reaches about 4000 cm ${}^2$ ·V ${}^{-1}$ ·s ${}^{-1}$ at room temperature, which is the highest among the compounds with an indirect bandgap of about 1.25 eV under the local density approximation. Our results can be the first guide for experiments to synthesize better two-dimensional materials for future semiconductor devices.

Besides its promising high electron mobilities at room temperature, PtSe₂ has a finite bandgap sensitively dependent on the number of monolayers combined by the van der Waals interaction according to our calculations based on the density functional theory. It was found that the frontier orbitals of the valence band maximum and the conduction band minimum are mainly contributed by p_z and p_x+y orbitals of Se, which are sensitive to the out-of-plane and the in-plane lattice constants, respectively. The van der Waals force enhances the bonding out-of-plane, which in turn influences the bonding in-plane. We explain that the layer number dependent bandgap has the same electronic reason as the strain dependent bandgap based on the scenario above. This work shows the flexibilities of tuning the electronic and optical properties of PtSe₂ in a wide range, which provides an advantage for applications of PtSe₂ in sensors.

The spin Hall conductivity (SHC) and anomalous Hall conductivity (AHC) in about 120 full Heusler compounds are calculated using the density functional theory in a high-throughput way. The electronic structures are mapped to the Wannier basis and the linear response theory is used to get the conductivity. Our results show that the mechanism under the SHC or AHC cannot be simply related to the valence electron numbers or atomic weights. It is related to the very details of the electronic structures, which can only be obtained by calculations. A high-throughput calculation is efficient to screen out the desired materials. According to our present results, Rh₂MnAl and Cu₂CoSn, as well as Co₂MnAl and Co₂MnGa are candidates in spintronic materials regarding their high SHC and AHC values, which can benefit the spin-torque-driven nanodevices.

The (001) surface of SrTiO₃ were transformed from insulating to conducting after Ar⁺ irradiation, producing a quasi two-dimensional electron gas (2DEG). This conducting surface layer can introduce Rashba spin orbital coupling due to the broken inversion symmetry normal to the plane. The spin splitting of such a surface has recently been demonstrated by magneto-resistance and angular resolved photoemission spectra measurements. Here, we present experiments evidencing a large spin-charge conversion at the conducting surface. We use spin pumping to inject a spin current from NiFe film into the surface, and measure the resulting charge current. The results indicate that the Rashba effect at the surface can be used for efficient charge-spin conversion. The conversion efficiency measured by the ratio of the spin flow density to the charge flow density is about 0.23 nm. This value is on the same order as the interfaces in metallic multilayers and 2DEG of LaAlO₃/SrTiO₃. In this point of view, the conducting SrTiO₃ surface provides another solution for oxide spintronics.