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Small-angle neutron scattering is used in combination with transport measurements to investigate the current-induced effects on the morphology of the intermediate mixed state domains in the intertype superconductor niobium. We report the robust self-organisation of the vortex lattice domains to elongated parallel stripes perpendicular to the applied current in a steady-state. The experimental results for the formation of the superstructure are supported by theoretical calculations, which highlight important details of the vortex matter evolution. The investigation demonstrates a mechanism of a spontaneous pattern formation that is closely related to the universal physics governing the intermediate mixed state in low-$kappa$ superconductors.
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A systematic study of irreversible magnetization was performed in bulk Niobium after different surface treatments. Starting with smooth surfaces and abrading them, a strong increase of the critical current is observed up an apparent limiting value. An impressive change of the critical current is also observed in the surface superconductivity (SSC) state, reaching values of the same order of magnitude as in the mixed state. We explain also the observation of strong SSC for magnetic field perpendicular to larges facets in terms of nucleation of SC along bumps of a corrugated surface.
The states of two phase-coupled superconducting rings have been investigated. Multiple current states have been revealed in the dependence of the critical current on the magnetic field. The performed calculations of the critical currents and energy states in a magnetic field have made it possible to interpret the experiment as the measurement of energy states into which the system comes with different probabilities because of the equilibrium and non-equilibrium noises upon the transition from the resistive state to the superconducting state during the measurement of the critical current
We present numerical solution of equations by Aslamazov and Lempitskiy (AL) for the distribution of the transport current density in thin superconducting films in the absence of external magnetic field, in both the Meissner and the vortex states. This solution describes smooth transition between the regimes of a wide film and a narrow channel and enables us to find the critical currents and current-voltage characteristics within a wide range of the film width and temperatures. We propose simple approximating formulas for the current density distributions and critical currents.
The Hall resistivity rho_{xy} of LuNi_2B_2C is negative in the normal as well as in the mixed state and has no sign reversal typical for high-T_c superconductors. A distinct nonlinearity in the rho_{xy} dependence on field H was found in the normal state for T < 40K, accompanied by a large magnetoresistance reaching +90% for mu_0H=16T at T=20K. The scaling relation rho_{xy} ~ rho_{xx}^beta (rho_{xx} is the longitudinal resistivity) was found in the mixed state, the value of beta being dependent on the degree of disorder.
We have studied hybrid superconducting micro-coolers made of a double Superconductor-Insulator-Normal metal tunnel junction. Under subgap conditions, the Andreev current is found to dominate the single-particle tunnel current. We show that the Andreev current introduces additional dissipation in the normal metal equivalent to Joule heating. By analyzing quantitatively the heat balance in the system, we provide a full description of the evolution of the electronic temperature with the voltage. The dissipation induced by the Andreev current is found to dominate the quasiparticle tunneling-based cooling over a large bias range.
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