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We experimentally investigate charge transport through the interface between a niobium superconductor and a three-dimensional WTe2 Weyl semimetal. In addition to classical Andreev reflection, we observe sharp non-periodic subgap resistance resonances. From an analysis of their positions, magnetic field and temperature dependencies, we can interpret them as an analog of Tomasch oscillations for transport along the topological surface state across the region of proximity-induced superconductivity at the Nb-WTe2 interface. Observation of distinct geometrical resonances implies a specific transmission direction for carriers, which is a hallmark of the Fermi arc surface states.

We experimentally investigate charge transport through a single planar junction between Cd3As2 Dirac semimetal and a normal Au lead. For non-superconducting bulk Cd3As2 samples, we observe non-Ohmic dV /dI(V ) curves, which strongly resemble standard Andreev reflection with well-defined superconducting gap. Andreev-like behavior is demonstrated for Cd3As2 samples with different surface and contact preparation techniques. We connect this behavior with surface superconductivity due to the flat-band formation in Cd3As2, which has been predicted theoretically. The conclusion on superconductivity is also supported by the gap suppression by magnetic fields or temperature.

We experimentally investigate transport properties of a hybrid structure, which consists of a thin single crystal SnSe flake on a top of 5 μm spaced Au leads. The structure initially is in highly conductive state, while it can be switched to the low-conductive one at high currents due to the Joule heating of the sample, which should be identified as phase transition to the symmetric β-Cmcm phase in SnSe. For the highly conductive state, there is significant hysteresis in dI/dV (V ) curves at low biases, so the sample conductance depends on the sign of the applied bias change. This hysteretic behavior reflects slow relaxation due to additional polarization current in the ferroelectric SnSe phase, which we confirm by direct measurement of time-dependent relaxation curves. In contrast, we observe no noticeable relaxation or low-bias hysteresis for the quenched low-conductive phase. Thus, the ferroelectric behavior can be switched on or off in transport through hybrid SnSe structure by controllable phase transition to the symmetric β-Cmcm phase. This result can also be important for nonvolatile memory development, e.g., phase change memory for neuromorphic computations or other applications in artificial intelligence and modern electronics.

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