We report a Rashba spin splitting of a two-dimensional electron gas in the topological insulator ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ from angle-resolved photoemission spectroscopy. We further demonstrate its electrostatic control, and show that spin splittings can be achieved which are at least an order-of-magnitude larger than in other semiconductors. Together these results show promise for the miniaturization of spintronic devices to the nanoscale and their operation at room temperature.

The electronic structure of epitaxial single-layer ${\mathrm{MoS}}_2$ on Au(111) is investigated by angle-resolved photoemission spectroscopy. Pristine and potassium-doped layers are studied in order to gain access to the conduction band. The potassium-doped layer is found to have a $(1.39\pm 0.05)\mathrm{eV}$ direct band gap at $\overline{K}$ with the valence band top at $\overline{\mathrm{\Gamma }}$ having a significantly higher binding energy than at $\overline{K}$. The moiré superstructure of the epitaxial system does not lead to the presence of observable replica bands or minigaps. The degeneracy of the upper valence band at $\overline{K}$ is found to be lifted by the spin-orbit interaction, leading to a splitting of $(145\pm 4)\mathrm{meV}$. This splitting is anisotropic and in excellent agreement with recent calculations. Finally, it is shown that the potassium doping does not only give rise to a rigid shift of the band structure but also to a distortion, leading to the possibility of band structure engineering in single-layers of transition metal dichalcogenides.

The electronic structure of epitaxial single-layer ${\mathrm{MoS}}_2$ on Au(111) is investigated by angle-resolved photoemission spectroscopy, scanning tunneling spectroscopy, and first-principles calculations. While the band dispersion of the supported single layer is close to a free-standing layer in the vicinity of the valence-band maximum at $\overline{K}$ and the calculated electronic band gap on Au(111) is similar to that calculated for the free-standing layer, significant modifications to the band structure are observed at other points of the two-dimensional Brillouin zone: at $\overline{\mathrm{\Gamma }}$, the valence-band maximum has a significantly higher binding energy than in the free ${\mathrm{MoS}}_2$ layer and the expected spin-degeneracy of the uppermost valence band at the $\overline{M}$ point cannot be observed. These band structure changes are reproduced by the calculations and can be explained by the detailed interaction of the out-of-plane ${\mathrm{MoS}}_2$ orbitals with the substrate.