D. V. Shovkun

Local noise in a diffusive conductor.

The control and measurement of local non-equilibrium configurations is of utmost importance in applications on energy harvesting, thermoelectrics and heat management in nano-electronics. This challenging task can be achieved with the help of various local probes, prominent examples including superconducting or quantum dot based tunnel junctions, classical and quantum resistors, and Raman thermography. Beyond time-averaged properties, valuable information can also be gained from spontaneous fluctuations of current (noise). From these perspective, however, a fundamental constraint is set by current conservation, which makes noise a characteristic of the whole conductor, rather than some part of it. Here we demonstrate how to remove this obstacle and pick up a local noise temperature of a current biased diffusive conductor with the help of a miniature noise probe. This approach is virtually noninvasive for the electronic energy distributions and extends primary local measurements towards strongly non-equilibrium regimes.

Anisotropy of normal resistivity in oxygen-deficient YBa2Cu3O7−x single crystals

Temperature dependences of the resistivity tensor components ρab and ρc were measured for YBa2Cu3O7−x single crystals with different oxygen contents. The resistivity anisotropy ρc/ρab was found to grow exponentially with decreasing temperature. The results are compared with the predictions of different models describing transverse transport in the normal state of cuprate high-Tc superconductors.

Anisotropy of the superconducting properties of YBa2Cu3O7−x single crystals with reduced oxygen content

In an investigation of the resistivity anisotropy of YBa2Cu3O7−x single crystals with suboptimal oxygen content it is observed that the superconducting transition for the component ρc of the resistivity tensor is shifted to lower temperatures with respect to the transition for the component ρab. A similar shift is also observed for the transition in the temperature dependence of the dynamic magnetic susceptibility.

Low-temperature resistivity of YBa2Cu3O6+x single crystals in the normal state

A scan of the superconductor-nonsuperconductor transformation in single crystals of YBa2Cu3O6+x (x≈0.37) is done in two alternative ways, namely, by applying a magnetic field and by reducing the hole concentration through oxygen rearrangement. The in-plane normal-state resistivity ρab obtained in the two cases is quite similar; its temperature dependence can be fitted by a logarithmic law in a temperature range of almost two decades. However, an alternative representation of the temperature dependence of σab=1/ ρ ab by a power law, typical for a 3D material near a metal-insulator transition, is also plausible. The vertical conductivity σc=1/ρc followed a power law, and neither σc(T), nor ρc(T) could be fitted by log T. It follows from the ρc measurements that the transformation at T=0 is split into two transitions: superconductor-normal-metal and normal-metal-insulator. In our samples, they are separated in oxygen content by Δx≈0.025.

c-axis penetration depth in Bi2Sr2CaCu2O8+δ single crystals measured by ac-susceptibility and cavity perturbation technique

The c-axis penetration depth Δλc in Bi2Sr2CaCu2O8+δ (BSCCO) single crystals as a function of temperature has been determined using two techniques, namely, measurements of the ac-susceptibility at a frequency of 100 kHz and the surface impedance at 9.4 GHz. Both techniques yield an almost linear function Δλc(T)∝T in the temperature range T<0.5Tc. Electrodynamic analysis of the impedance anisotropy has allowed us to estimate λc(0)≈50 µm in BSCCO crystals overdoped with oxygen (Tc≈84 K) and λc(0)≈150 µm at the optimal doping level (Tc≈90 K).

Shot noise of the edge transport in the inverted band HgTe quantum wells

We investigate the current noise in HgTe-based quantum wells with an inverted band structure in the regime of disordered edge transport. Consistent with previous experiments, the edge resistance strongly exceeds h/e2 and weakly depends on the temperature. The shot noise is well below the Poissonian value and characterized by the Fano factor with gate voltage and sample-to-sample variations in the range 0.1 < F < 0.3. Given the fact that our devices are shorter than the most pessimistic estimate of the ballistic dephasing length, these observations exclude the possibility of one-dimensional helical edge transport. Instead, we suggest that a disordered multi-mode conduction is responsible for the edge transport in our experiment.

Nonlinear transport and noise thermometry in quasiclassical ballistic point contacts

We study nonlinear transport and non-equilibrium current noise in quasi-classical point contacts (PCs) defined in a low-density high-quality two-dimensional electron system in GaAs. At not too high bias voltages

Noise thermometry applied to thermoelectric measurements in InAs nanowires

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Andreev Reflection in an s-Type Superconductor Proximized 3D Topological Insulator.

across the PC the noise temperature is determined by a Joule heat power and almost independent on the PC resistance that can be associated with a self-heating of the electronic system. This commonly accepted scenario breaks down at increasing

Finite-size effect in shot noise in hopping conduction

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