The semiconducting properties of most 2D magnets investigated so far, however, are strongly affected by the extremely narrow widths of their conduction and valence bands, typically a few tens of meV or less. [7][8][9][10][11][12][13] Such narrow bandwidths cause electron localization and prevent low-temperature conductivity measurements, which is why transport experiments probing the magnetic properties of 2D semiconductors have been so far limited to studies of tunneling through atomically thin multilayer barriers. [14][15][16][17][18][19][20][21] CrSBr [22] (see Figure 1a)-a recently introduced 2D magnetic semiconductor-appears to be an exception. [23,24] First-principles calculations (shown in Figure 1b) predict its conduction band to have a width of ≈1.5 eV. [24,25] Accordingly, low-temperature in-plane magnetoresistance measurements (see Figure 1c,d) could be performed successfully, and analyzed to determine the magnetic phase diagram. [23] The unique magnetic properties of this material have been further showcased by experiments on van der Waals (vdW) interfaces, in which CrSBr was found to imprint into an adjacent graphene layer a giant exchange interaction, much stronger than what has been reported in earlier work on analogous heterostructures. [26] Electronic transport through exfoliated multilayers of CrSBr, a 2D semiconductor of interest because of its magnetic properties, is investigated. An extremely pronounced anisotropy manifesting itself in qualitative and quantitative differences of all quantities measured along the in-plane a and b crystallographic directions is found. In particular, a qualitatively different dependence of the conductivities σ a and σ b on temperature and gate voltage, accompanied by orders of magnitude differences in their values (σ b /σ a ≈ 3 × 10 2 to 10 5 at low temperature and negative gate voltage) are observed, together with a different behavior of the longitudinal magnetoresistance in the two directions and the complete absence of the Hall effect in transverse resistance measurements. These observations appear not to be compatible with a description in terms of conventional band transport of a 2D doped semiconductor. The observed phenomenology-and unambiguous signatures of a 1D van Hove singularity detected in energy-resolved photocurrent measurements-indicate that electronic transport through CrSBr multilayers is better interpreted by considering the system as formed by weakly and incoherently coupled 1D wires, than by conventional 2D band transport. It is concluded that CrSBr is the first 2D semiconductor to show distinctly quasi-1D electronic transport properties.

Two-dimensional materials have significant potential for the development of new devices.Here we report the electronic and structural properties of β -GeSe, a previously unreported polymorph of GeSe, with a unique crystal structure that displays strong two-dimensional structural features. β -GeSe is made at high pressure and temperature and is stable under ambient conditions. We compare it to its structural and electronic relatives α-GeSe and black phosphorus. The β form of GeSe displays a boat conformation for its Ge-Se six-ring, while the previously known α form, and black phosphorus, display the more common chair conformation for their six-rings. Electronic structure calculations indicate that β -GeSe is a semiconductor, with an approximate bulk band gap of ∆ ≈ 0.5 eV, and, in its monolayer form, ∆ ≈ 0.9 eV. These * To whom correspondence should be addressed values fall between those of α-GeSe and black phosphorus, making β -GeSe a promising candidate for future applications. The resistivity of our β -GeSe crystals measured in-plane is on the order of ρ ≈ 1 Ωcm, while being essentially temperature independent.

We have synthesized previously unreported high-entropy alloys (HEAs) in the pentanary (ScZrNb)1–x [RhPd] x and hexanary (ScZrNbTa)1–x [RhPd] x systems. The materials have CsCl-type structures and mixed site occupancies. Both HEAs are type-II superconductors with strongly varying critical temperatures (T c’s) depending on the valence electron count (VEC); the T c’s increase monotonically with decreasing VEC within each series, and do not follow the trends seen for either crystalline or amorphous transition metal superconductors. The (ScZrNb)0.65[RhPd]0.35 HEA with the highest T c, ∼9.3 K, also exhibits the largest μ0 H c2(0) = 10.7 T. The pentanary and hexanary HEAs have higher superconducting transition temperatures than their simple binary intermetallic relatives with the CsCl-type structure and a surprisingly ductile mechanical behavior. The presence of niobium, even at the 20% level, has a positive impact on the T c. Nevertheless, niobium-free (ScZr)0.50[RhPd]0.50, as mother-compound of both superconducting HEAs found here, is itself superconducting, proving that superconductivity is an intrinsic feature of the bulk material.

Nodal-line semimetals are topologically nontrivial states of matter featuring band crossings along a closed curve, i.e., nodal-line, in momentum space. Through a detailed analysis of the electronic structure, we show, for the first time, that the normal state of the superconductor NaAlSi, with a critical temperature of Tc ≈ 7 K, is a nodal-line semimetal, where the complex nodal-line structure is protected by nonsymmorphic mirror crystal symmetries. We further report on muon spin rotation experiments revealing that the superconductivity in NaAlSi is truly of bulk nature, featuring a fully gapped Fermi-surface. The temperature-dependent magnetic penetration depth can be well described by a two-gap model consisting of two s-wave symmetric gaps with Δ1 = 0.6(2) meV and Δ2 = 1.39(1) meV. The zero-field muon experiment indicates that time-reversal symmetry is preserved in the superconducting state. Our observations suggest that, notwithstanding its topologically nontrivial band structure, NaAlSi may be suitably interpreted as a conventional London superconductor, while more exotic superconducting gap symmetries cannot be excluded. The intertwining of topological electronic states and superconductivity renders NaAlSi a prototypical platform to search for unprecedented topological quantum phases.

In the transition metal dichalcogenide IrTe 2 , low-temperature charge-ordered phase transitions involving Ir dimers lead to the occurrence of stripe phases of different periodicities, and nearly degenerate energies. Bulksensitive measurements have shown that, upon cooling, IrTe 2 undergoes two such first-order transitions to (5 × 1 × 5) and (8 × 1 × 8) reconstructed phases at T c 1 ∼ 280 K and T c 2 ∼ 180 K, respectively. Here, using surface sensitive probes of the electronic structure of IrTe 2 , we reveal the first-order phase transition at T c 3 = 165 K to the (6 × 1) stripes phase, previously proposed to be the surface ground state. This is achieved by combining x-ray photoemission spectroscopy and angle-resolved photoemission spectroscopy, which give access to the evolution of stripe domains and a particular surface state, the energy of which is dependent on the Ir dimer length. By performing measurements over a full thermal cycle, we also report the complete hysteresis of all these phases.