There is a growing interest in the recent years toward developing wide gap semiconductor nanostructures, and a lot of efforts have been dedicated to ZnO. In order to design core shell structures, a larger bandgap material is needed, which would ideally be similarly environment friendly. ZnS is an interesting possibility and although some efforts were devoted to it in the literature, its properties are not yet fully understood and precisely measured. In this work, we make a thorough analysis of high quality ZnS epilayers, in order to precisely determine the basic optical properties related to excitons and impurities in ZnS. We have made the first precise quantitative determination of residual strain using high-resolution x-ray diffraction. This allows us to demonstrate that, as it was hypothesized in most previous works, thermoelastic strain originating from the layer-substrate expansion coefficient mismatch is responsible for shifts and splitting of exciton photoluminescence lines. The identification of the bound excitons’ optical transitions is analyzed through their temperature/power dependence, in order to precisely assess their exact nature. Combined with the careful determination of donor and acceptor ionization energies in our ZnS sample, we discard the possibility of sodium as the main residual acceptor, as it has often been proposed in the literature.

We have produced thin film samples of cubic ZnS by the chemical bath method. These samples were synthesized using zinc chloride, thiourea, sodium citrate and ammonia solutions at varied deposition time from 24h to 96h. X-ray diffraction (XRD), transmittance and photoluminescence (PL) analyses provided the physical characteristics of cubic ZnS films with crystal plane orientations (2 0 0) and (2 2 2), lattice parameters of 5.648 Å and an atomic plane distance d=1.412 Å. The grain size calculed are 16.53 nm and 17.12 nm. PL revealed deep defects in the gap with peaks in the visible, with prominent emissions at 430 nm (blue) and 510 nm (green). The measured transmittance of the films is 88.6%.

It has recently been shown that Terahertz sensors can effectively detect the spin resonances of Dirac fermions in graphene. The associated photovoltaic measurement technique allows for the investigation of the intrinsic spin-orbit coupling in graphene as well as its topological properties from microwave to Terahertz frequencies. In this work, using graphene/MoS₂-based Field-Effect Transistors, we observed a magnetic resonance photovoltage signal in the Gigahertz range that is independent on the gate bias. The dispersion of the associated spin-flip transitions remains intriguingly unaffected by the MoS₂ layer. In parallel, the spin-related signal consistently appears as a drop in photovoltage, regardless of the signal's polarity or origin, whether it is due to plasma wave rectification or thermoelectric effects. This behavior is interpreted as a decrease in the system's spin polarization due to spin-dependent recombination or scattering of photocarriers. Understanding the various photovoltaic signals in highly sensitive Gigahertz/Terahertz sensors paves the way for exploring spin-dependent mechanisms in two-dimensional quantum materials, influenced by proximity effects such as spin-orbit coupling, topology, and magnetism.

In a 2D electron system (2DES) the breaking of the inversion, time‐reversal and bulk crystal‐field symmetries is interlaced with the effects of spin‐orbit coupling (SOC) triggering exotic quantum phenomena. Here, epitaxial engineering is used to design and realize a 2DES characterized simultaneously by ferromagnetic order, large Rashba SOC and hexagonal band warping at the (111) interfaces between LaAlO 3 , EuTiO 3 , and SrTiO 3 insulators. The 2DES displays anomalous quantum corrections to the magneto‐conductance driven by the time‐reversal‐symmetry breaking occurring below the magnetic transition temperature. The results are explained by the emergence of a non‐trivial Berry phase and competing weak anti‐localization/weak localization back‐scattering of Dirac‐like fermions, mimicking the phenomenology of gapped topological insulators. These findings open perspectives for the engineering of novel spin‐polarized functional 2DES holding promises in spin‐orbitronics and topological electronics.

By using the self-consistent Born approximation, we investigate disorder effect induced by shortrange impurities on the band-gap of a seminal two-dimensional (2D) system, whose phase diagram contains trivial, single-band-inverted and double-band-inverted states. Following the density-ofstates (DOS) evolution, we demonstrate multiple closings and openings of the band-gap with the increase of the disorder strength. Calculations of the spectral function describing the quasiparticles at the Γ point of the Brillouin zone evidence that the observed band-gap behavior is unambiguously caused by the topological phase transitions due to the mutual inversions between the first and second electron-like and hole-like subbands. We also find that an increase in the disorder strength in the double-inverted state always leads to the band-gap closing due to the overlap of the tails of DOS from conduction and valence subbands.