The quantum spin Hall effect (QSHE), a hallmark of topological insulators, enables dissipationless, spin-polarized edge transport and has been predicted in various two-dimensional materials. However, challenges such as limited scalability, low-temperature operation, and the lack of robust electronic transport have hindered practical implementations. Here, we demonstrate the QSHE in an InAs/GaInSb/InAs trilayer quantum well structure operating at elevated temperatures. This platform meets key criteria for device integration, including scalability, reproducibility, and tunability via electric field. When the Fermi level is positioned within the energy gap, we observe quantized resistance values independent of device length and in both local and nonlocal measurement configurations, confirming the QSHE. Helical edge transport remains stable up to T = 60 kelvin, with further potential for higher-temperature operation. Our findings establish the InAs/GaInSb system as a promising candidate for integration into next-generation devices harnessing topological functionalities, advancing the development of topological electronics.

Among the different methods to grow graphene on silicon carbide (SiC), the chemical vapor deposition (CVD) in a hydrogen atmosphere has several interesting features arising from the use of this gas. Despite its versatility and its ability to grow graphene with a quality allowing applications in electrical metrology, this synthesis method remains largely understudied. This work is specifically dedicated to this growth technique in conditions leading to the epitaxy of graphene on a buffer layer. We first show that hydrogen has several effects during the cooling down, possibly leading to hydrogen intercalation beneath graphene, or even to graphene etching. Then, we use a specific cooling under argon, allowing the suppression of hydrogen effects, to follow the successive phases of the graphene formation, from the nucleation of islands and ribbons to their coalescence on SiC. Finally, we demonstrate that graphene growth is, in our growth conditions, self-limited to a unique monolayer.

Defects in crystals can have a transformative effect on the properties and functionalities of solid-state systems. Dopants in semiconductors are core components in electronic and optoelectronic devices. The control of single color centers is at the basis of advanced applications for quantum technologies. Unintentional defects can also be detrimental to the crystalline structure and hinder the development of novel materials. Whatever the research perspective, the identification of defects is a key, but complicated, and often long-standing issue. Here, we present a general methodology to identify point defects by combining isotope substitution and polytype control, with a systematic comparison between experiments and first-principles calculations. We apply this methodology to hexagonal boron nitride ( h -BN) and its ubiquitous color center emitting in the ultraviolet spectral range. From isotopic purification of the host h -BN matrix, a local vibrational mode of the defect is uncovered, and isotope-selective carbon doping proves that this mode belongs to a carbon-based center. Then, by varying the stacking sequence of the host h -BN matrix, we unveil different optical responses to hydrostatic pressure for the nonequivalent configurations of this ultraviolet color center. We conclude that this defect is a carbon dimer in the honeycomb lattice of h -BN. Our results show that tuning the stacking sequence in different polytypes of a given crystal provides unique fingerprints contributing to the identification of defects in 2D materials.

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.