Simulation of the Heat Transfer Process of Superconducting Films in the Resistive State

Technical Physics - The heat transfer in a contact–film–substrate system was analyzed under conditions in which the heat removal from a sample to the substrate is insufficient to avoid...     

Upper critical field of niobium nitride thin films

The temperature dependences of the superconducting transition of niobium nitride (NbN) thin films have been investigated via the first harmonic of the voltage in dc magnetic fields of up to 8 T. The temperature dependence of the second critical field of NbN has been determined. The parameter responsible for the effect of spin paramagnetism in this material and the temperature dependence of the upper critical field that describes well the experimental data have been found in terms of the Werthamer–Helfand–Hohenberg (WHH) theory. The key parameters of the superconductor have been estimated from the transport and optical measurements.     

Synthesis of magnesium silicate by heat treatment of sols and mechanical activation of solid components

A layered magnesium silicate, an analog to natural talc, was synthesized by mechanical treatment of a mixture of magnesium hydroxide and hydrated silicic acid powders, as well as by heat treatment of aqueous dispersions containing magnesium hydroxide particles and silica sols prepared from different precursors.     

Size dependence of the transmittance for metal nanofilms in the infrared region

The transmission of infrared electromagnetic waves through quasi-homogeneous thin metal films is investigated within the diagonal response approximation. An expression for the dielectric function is derived in the framework of the finite-depth potential well model with due regard for the size dependence of the Fermi energy. The transmittance of the films is calculated, and the results of the calculations are compared with experimental data. The calculations are performed for Al, Au, and Ag.     

New experimental criterion of the Berezinskii-Kosterlitz-Thouless transition

Based on the experimental study of YBa₂Cu₃O_7?x single crystal nonlinearity near T _c , a new criterion for observing the Berezinskii-Kosterlitz-Thouless (BKT) transition in cuprate HTSC compounds was proposed. The criterion consists in the existence of the maximum in the dependence of the voltage of the second harmonic of the sample response signal excited by alternating current on the direct bias current. It was shown that the position of the second harmonic maximum is independent of temperatures near T _c , which is consistent with the BKT transition independence of the measuring current.     

Critical Phase-Transition Current in Niobium Nitride Thin Films

Physics of the Solid State - Abstract—The effect of current and magnetic field on the transition to the superconducting state in niobium nitride thin films has been studied. The critical...     

Quantum-size effects on the characteristics of single-electron tunneling

Effects of single-electron tunneling charging and Coulomb blockade in a cluster structure (molecular transistor) with regard to the quantization of electron levels in an island electrode are investigated. The spectrum of electrons is calculated for small disk-shaped clusters. Restrictions connected with the Coulomb instability of the cluster and electron relaxation are introduced in the theory. The current gap and its voltage asymmetry are calculated for single-electron transistors based on small gold clusters. The effect of the cluster shape on the current gap is investigated.     

Magnetic Field Gain in Vortex Pinning at Fractal Interfaces of Clusters of High-Temperature Superconductors

Technical Physics - The effect of the fractality of the cluster interfaces in the normal phase of a copper-oxide high-temperature superconductor YBCO on the magnetic creep has been studied. The...     

Current-voltage characteristics of YBa2Cu3O7−x single crystals and Kosterlitz-Thouless transition

The nonlinear I-V characteristic (V(I)) of YBa₂Cu₃O_7−x single crystal was investigated near the transition from the resistive to the superconducting state in the absence of a magnetic field. A modulation Fourier analysis at temperature T* (the maximum of the amplitudes of the higher (n>1) harmonics of the response voltage) was used to determine an analytic dependence V(I) which accurately describes the experimental results (direct measurements and harmonics) in the range of currents I<30 mA (j<310 A/cm²). It is shown that at T* the power approximation of the I-V characteristic V∼I ³ is only found in the low current density limit (j≪j ₀=140 A/cm²). The results are interpreted in terms of the Kosterlitz-Thouless (KT) transition model. It is established that T* corresponds to the temperature of the KT transition T _KT, which means that T _KT can be determined directly. The deviation of V(I) from a power dependence is caused by the nonlogarithmic variation of the vortex interaction energy as a function of the distance between them. Fiz. Tverd. Tela (St. Petersburg) 40, 202–204 (February 1998)