The layered van der Waals antiferromagnet ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ has been predicted to combine the band ordering of archetypical topological insulators such as ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ with the magnetism of Mn, making this material a viable candidate for the realization of various magnetic topological states. We have systematically investigated the surface electronic structure of ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$(0001) single crystals by use of spin- and angle-resolved photoelectron spectroscopy experiments. In line with theoretical predictions, the results reveal a surface state in the bulk band gap and they provide evidence for the influence of exchange interaction and spin-orbit coupling on the surface electronic structure.

We predict ${\mathrm{NiTe}}_2$ to be a type-II Dirac semimetal based on ab initio calculations and explore its bulk and spin-polarized surface states using spin- and angle-resolved photoemission spectroscopy (spin-ARPES). Our results show that, unlike ${\mathrm{PtTe}}_2, {\mathrm{PtSe}}_2$, and ${\mathrm{PdTe}}_2$, the Dirac node in ${\mathrm{NiTe}}_2$ is located in close vicinity to the Fermi energy. Additionally, ${\mathrm{NiTe}}_2$ also hosts a pair of band inversions below the Fermi level along the $\mathrm{\Gamma }-A$ high-symmetry direction, with one of them leading to a Dirac cone in the surface states. The bulk Dirac nodes and the ladder of band inversions in ${\mathrm{NiTe}}_2$ support unique topological surface states with chiral spin texture over a wide range of energies. Our work paves the way for the exploitation of the low-energy type-II Dirac fermions in ${\mathrm{NiTe}}_2$ in the fields of spintronics, infrared plasmonics, and ultrafast optoelectronics.

The advent of topological semimetals enables the exploitation of symmetry-protected topological phenomena and quantized transport. Here, we present homogeneous rectifiers, converting high-frequency electromagnetic energy into direct current, based on low-energy Dirac fermions of topological semimetal-NiTe₂, with state-of-the-art efficiency already in the first implementation. Explicitly, these devices display room-temperature photosensitivity as high as 251 mA W⁻¹ at 0.3 THz in an unbiased mode, with a photocurrent anisotropy ratio of 22, originating from the interplay between the spin-polarized surface and bulk states. Device performances in terms of broadband operation, high dynamic range, as well as their high sensitivity, validate the immense potential and unique advantages associated to the control of nonequilibrium gapless topological states via built-in electric field, electromagnetic polarization and symmetry breaking in topological semimetals. These findings pave the way for the exploitation of topological phase of matter for high-frequency operations in polarization-sensitive sensing, communications and imaging.

Quantum materials are central for the development of novel functional systems that are often based on interface specific phenomena. Fabricating controlled interfaces between quantum materials requires adopting a flexible growth technique capable to synthesize different materials within a single-run deposition process with high control of structure, stoichiometry, and termination. Among the various available thin film growth technologies, pulsed laser deposition (PLD) allows controlling the growth of diverse materials at the level of single atomic layers. In PLD the atomic species are supplied through an ablation process of a stoichiometric target either in form of polycrystalline powders or of a single crystal. No carrier gases are needed in the deposition process. The ablation process is compatible with a wide range of background pressure. We present results of thin-film growth by PLD obtained by using an Nd:YAG infrared pulsed laser source operating at its first harmonics. With respect to the traditional PLD systems—based on excimer KrF UV-lasers—optimal conditions for the growth of thin films and heterostructures are reached at large target-to-substrate distance. Merits and limitations of this approach for growing oxide and non-oxide thin films are discussed. The merits of an Nd:YAG laser to grow very high-quality thin films suggest the possibility of implementing compact in-situ setups e.g. integrated with analytical instrumentation under ultra-high vacuum conditions.

High-pressure x-ray diffraction measurements have been carried out on the intermetallic semiconductor ${\mathrm{FeGa}}_3$ and the equation of state for ${\mathrm{FeGa}}_3$ has been determined. First-principles based DFT calculations within the GGA approximation indicate that although the unit cell volume matches well with the experimentally obtained value at ambient pressure, it is significantly underestimated at high pressures and the difference between them increases as pressure increases. $\mathrm{GGA}+U$ calculations with increasing values of $U_{\mathrm{Fe}\left(3d\right)}$ (on-site Coulomb repulsion between the Fe $3d$ electrons) at high pressures, correct this discrepancy. Further, the $\mathrm{GGA}+U$ calculations also show that along with $U_{\mathrm{Fe}\left(3d\right)}$, the Fe $3d$ bandwidth also increases with pressure and around a pressure of 4 GPa, a small density of states appear at the Fermi level. High-pressure resistance measurements carried out on ${\mathrm{FeGa}}_3$ also clearly show a signature of an electronic transition. Beyond the pressure of 19.7 GPa, the diffraction peaks reduce in intensity and are not observable beyond $\sim 26\mathrm{GPa}$, leading to an amorphous state.