The van-der-Waals material CrSBr stands out as a promising two-dimensional magnet. Here, we report on its detailed magnetic and structural characteristics. We evidence that it undergoes a transition to an A-type antiferromagnetic state below T_N ≈ 140 K with a pronounced two-dimensional character, preceded by ferromagnetic correlations within the monolayers. Furthermore, we unravel the low-temperature hidden-order within the long-range magnetically-ordered state. We find that it is associated to a slowing down of the magnetic fluctuations, accompanied by a continuous reorientation of the internal field. These take place upon cooling below T_s ≈ 100 K, until a spin freezing process occurs at T* ≈ 40 K. We argue this complex behavior to reflect a crossover driven by the in-plane uniaxial anisotropy, which is ultimately caused by its mixed-anion character. Our findings reinforce CrSBr as an important candidate for devices in the emergent field of two-dimensional magnetic materials.

High-entropy alloys (HEAs) are a new class of materials constructed from multiple principal elements statistically arranged on simple crystallographic lattices. Due to the large amount of disorder present, they are excellent model systems for investigating the properties of materials intermediate between crystalline and amorphous states. Here we report the effects of systematic isoelectronic replacements, using Mo-Y, Mo-Sc, and Cr-Sc mixtures, for the valence electron count 4 and 5 elements in the body-centered cubic (BCC) Ta-Nb-Zr-Hf-Ti high-entropy alloy (HEA) superconductor. We find that the superconducting transition temperature $T_{\mathrm{c}}$ strongly depends on the elemental makeup of the alloy, and not exclusively its electron count. The replacement of niobium or tantalum by an isoelectronic mixture lowers the transition temperature by more than 60%, while the isoelectronic replacement of hafnium, zirconium, or titanium has a limited impact on $T_{\mathrm{c}}$. We further explore the alloying of aluminium into the nearly optimal electron count ${\left[\mathrm{TaNb}\right]}_{0.67}{\left(\mathrm{ZrHfTi}\right)}_{0.33}$ HEA superconductor. The electron count dependence of the superconducting $T_{\mathrm{c}}$ for ${\left(\mathrm{HEA}\right)\mathrm{Al}}_x$ is found to be more crystallinelike than for the ${\left[\mathrm{TaNb}\right]}_{1-x}{\left(\mathrm{ZrHfTi}\right)}_x$ HEA solid solution. For an aluminum content of $x=0.4$ the high-entropy stabilization of the simple BCC lattice breaks down. This material crystallizes in the tetragonal $\beta$-uranium structure type and superconductivity is not observed above 1.8 K.

Strain is ubiquitous in solid-state materials, but despite its fundamental importance and technological relevance, leveraging externally applied strain to gain control over material properties is still in its infancy. In particular, strain control over the diverse phase transitions and topological states in two-dimensional transition metal dichalcogenides remains an open challenge. Here, we exploit uniaxial strain to stabilize the long-debated structural ground state of the 2D topological semimetal IrTe₂, which is hidden in unstrained samples. Combined angle-resolved photoemission spectroscopy and scanning tunneling microscopy data reveal the strain-stabilized phase has a 6 × 1 periodicity and undergoes a Lifshitz transition, granting unprecedented spectroscopic access to previously inaccessible type-II topological Dirac states that dominate the modified inter-layer hopping. Supported by density functional theory calculations, we show that strain induces an Ir to Te charge transfer resulting in strongly weakened inter-layer Te bonds and a reshaped energetic landscape favoring the 6×1 phase. Our results highlight the potential to exploit strain-engineered properties in layered materials, particularly in the context of tuning inter-layer behavior.

We report on the phase formation and the superconducting properties in the NbS₂ system. Specifically, we have performed a series of standardized solid-state syntheses in this system, which allow us to establish a comprehensive synthesis map for the formation of the two polytypes 2H-NbS₂ and 3R-NbS₂, respectively. We show that the identification of two polytypes by means of X-ray diffraction is not always unambiguous. Our physical property measurements on a phase-pure sample of 3R-NbS₂, on a phase-pure sample of 2H-NbS₂, and a mixed phase sample confirm earlier reports that 2H-NbS₂ is a bulk superconductor and that 3R-NbS₂ is not a superconductor above T = 1.75 K. Our results clearly show that specific heat measurements, as true bulk measurements, are crucial for the identification of superconducting materials in this and related systems. Our results indicate that for the investigation of van der Waals materials great care has to be taken on choosing the synthesis conditions for obtaining phase pure samples.

Pressure effect in NbSe ₂ resembles hallmark features of unconventional superconductivity in cuprates.