Dynamical properties near the metal-insulator transition: evidence for electron-assisted variable range hopping

High-Entropy van der Waals Materials Formed from Mixed Metal Dichalcogenides, Halides, and Phosphorus Trisulfides

The charge, spin, and composition degrees of freedom in a high-entropy alloy endow it with tunable valence and spin states, infinite combinations, and excellent mechanical performance. Meanwhile, the stacking, interlayer, and angle degrees of freedom in a van der Waals material bring to it exceptional features and technological applications. Integration of these two distinct material categories while keeping their merits would be tempting. On the basis of this heuristic thinking, we design and explore a new range of materials (i.e., dichalcogenides, halides, and phosphorus trisulfides) with multiple metallic constitutions and intrinsic layered structure, which are coined as high-entropy van der Waals materials. Millimeter-scale single crystals with a homogeneous element distribution can be efficiently acquired and easily exfoliated or intercalated in this materials category. Multifarious physical properties such as superconductivity, magnetic ordering, metal-insulator transition, and corrosion resistance have been exploited. Further research based on the concept of high-entropy van der Waals materials will enrich the high-throughput design of new systems with intriguing properties and practical applications.

Suppression of inelastic electron-electron scattering in anderson insulators

We report on measurements of absorption from applied ac fields in Anderson-localized indium-oxide films. The absorption shows a roll-off at a frequency that is much smaller than the electron-electron scattering rate measured at the same temperature in diffusive samples of this material. These results are interpreted as evidence for discreteness of the energy spectrum.

Measurements of the complex conductivity of NbxSi(1-x) alloys on the insulating side of the metal-insulator transition

We have conducted temperature and frequency dependent transport measurements in amorphous NbxSi1-x samples in the insulating regime. We find a temperature dependent dc conductivity consistent with variable range hopping in a Coulomb glass. The frequency dependent response in the millimeter-wave frequency range can be described by the expression sigma(omega) varies with (-iota omega)(alpha) with the exponent somewhat smaller than 1. Our ac results are not consistent with extant theories for the hopping transport.

Hot-electron effects in two-dimensional hopping with a large localization length

We have studied nonlinear effects in the resistance of a two-dimensional system with a large localization length on both sides of the crossover from weak to strong localization. It is shown that nonlinearity in the hopping regime is due to electron overheating rather than the field effects. This qualitatively new behavior is a signature of a two-dimensional hopping transport with a large localization length.