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Non-reciprocity in the critical current has been observed in a variety of superconducting systems and has been called the superconducting diode effect. The origin underlying the effect depends on the symmetry breaking mechanisms at play. We investigate superconducting micro-bridges of NbN and also NbN/magnetic insulator (MI) hybrids. We observe a large diode efficiency of [Formula: see text]30% when an out-of-plane magnetic field as small as 25 mT is applied. In both NbN and NbN/MI hybrid, we find that the diode effect vanishes when the magnetic field is parallel to the sample plane. Our observations are consistent with the critical current being determined by the vortex surface barrier. Unequal barriers on the two edges of the superconductor strip result in the diode effect. Furthermore, the rectification is observed up to 10 K, which makes the device potential for diode based applications over a larger temperature range than before.

Contact resistances of multiwalled nanotubes deposited on gold contact fingers are very large. We show that the contact resistances decrease by orders of magnitudes when the contact areas are selectively exposed to the electron beam in a scanning electron microscope. The focused electron beam enables the selection of one particular nanotube for electrical measurement in a four-terminal configuration, even if a loose network of nanotubes is deposited on the gold electrodes. For all measured nanotubes, resistance values lie in a narrow range of 0.35–2.6 kΩ at room temperature.

We have investigated the electron heating in metallic diffusive wires of varying length at liquid-helium temperature by measuring the electric noise. The local increase of the electron temperature can be essential already for small currents and is well described by a heat-diffusion equation for the electrons. Depending on the electron thermal conductance and the electron–phonon coupling in the wire, different length regimes are identified. The quantitative knowledge of the electron temperature is important for analysis of nonequilibrium effects involving current heating in mesoscopic wires.

We investigate transport properties of superconducting TiN films in the vicinity of the superconductor-insulator transition (SIT). We show that the current - voltage (I - V) characteristics are mirror-symmetric with respect to the SIT and can be switched to each other by the applied magnetic field. In both superconducting and insulating states the low-temperature I - V characteristics have pronounced diode-like threshold character, demonstrating voltage/current jumps over several orders of magnitude at the corresponding critical current or threshold voltage. We have found that for both states the theory developed for Josephson junction arrays offers a quantitative description of the experimental results.

We report on the preparation of carbon nanotube quantum dots using superconducting electrodes made of niobium. Gate-controllable supercurrents with values of up to 30 nA are induced by the proximity effect. The IV-curves are hysteretic at low temperature and the corresponding switching histograms have a width of ~0.5-2. An on-chip resistive environment integrated in the sample layout is used in order to increase the switching current.