A. I. Ponomarev

Quasi-two-dimensional transport properties of the layered superconductor Nd2−xCe x CuO4+δ

AbstractThe temperature dependences of resistivities ρab in the ab plane and ρc along the c axis have been studied for single-crystal Nd2 − xCexCuO4 + δ (x = 0.12, 0.15, 0.17, 0.20) films with (001) and (1

Effect of disorder on the transport properties of the high-Tc superconductor Nd2− xCexCuO4+δ

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On the nature of the anisotropy of the resistivity of Nd2−xCexCuO4+δ with different cerium and oxygen concentrations

0) orientations. The superconducting transition temperature and anisotropy coefficient are shown to be maximal in optimally annealed samples (the oxygen content is close to the stoichiometric content, δ → 0). A combination of the metallic behavior of the ρab(T) dependence and the nonmetallic behavior of the ρc(T) dependence for the optimally annealed samples is an intrinsic property of the substance and an indication of the fact that the system is quasi-two-dimensional. This layered quasi-two-dimensional system is an Anderson dielectric with a strongly anisotropic localization radius (Rlocab ≫ Rlocc). An increase in the oxygen content and, hence, in the degree of disorder in the Nd2 − xCexCuO4 + δ system is found to decrease the resistivity anisotropy coefficient. Thus, a disorder-induced Anderson transition takes place in this quasi-two-dimensional system.

Anisotropy of transport properties of layered superconductors Nd2− x Ce x CuO4 + δ and Ca2 − x Sr x RuO4

The effect of low-temperature decomposition of the nonstoichiometric (in oxygen) Ba2YCu3O7−δ phase on the critical characteristics of ceramic has been studied. The decomposition taking place in this system was found to occur via a spinodal mechanism. As a result of the decomposition, oxygen-depleted particles were shown to be formed in samples that are relatively rich in oxygen. These particles can play the role of pinning centers, which manifests itself in improving the dependence of the critical current density on the magnetic field.

Two-dimensional weak localization effects in high temperature superconductor Nd2−xCexCuO4−δ

The temperature dependences ρab(T) of Nd2−xCexCuO4+δ single crystals with 0≤x≤0.20 are studied and analyzed on the basis of the concepts in the theory of disordered 2D systems. The results are compared with the data obtained for other copper-oxide HTSC. It is found that a transition to the superconducting state in the optimal doping region 0.14≤x≤0.18 occurs only in crystals with a fairly small degree of disorder (kFl≥2, where l is the mean free path). This transition is compatible with the weak 2D-localization mode as long as the localization radius is longer than the characteristic size of a Cooper pair. The superconducting transition temperature in the optimal doping region increases monotonically with the parameter kFl characterizing the degree of disorder in the crystal. The degradation of superconducting properties upon a further increase in the doping level (x>0.18) is apparently associated with a transition from 2D to 3D conductivity in the single crystal.

Anisotropy of the electrical resistivity of Nd2-xCexCuO4 +δSingle crystals with different contents of the doping component

Resistive and magnetic measurements are made on La1.85−4∕3xSr0.15+4∕3xCu1−xMnxO4 ceramics with x=0.02, 0.04, 0.06, and 0.08. It is found that at these concentrations the temperature of the beginning and end of the superconducting transition depend weakly on the concentration x. The resistive properties exhibit a combination of metallic conductivity (or superconductivity) along the grains with hopping transport between grains. At low temperatures the superconductivity apparently coexists with two different magnetic phases.

Effect of low-temperature decomposition on the resistive properties of Ba 2 YCu 3

The results of a study of the temperature dependences of the resistivity and its anisotropy coefficient in the normal phase of single-crystal Nd2−xCexCuO4+δ films with different degrees of cerium doping x and oxygen content δ are presented. Two types of films of identical composition are considered, grown with the orientation of the c axis of the crystal perpendicular to and parallel to the plane of the substrate. The parameters found from an analysis of the conductivity and Hall coefficient are presented for the 18 samples studied.

Quasi-two-dimensional transport properties of the layered superconductor Nd 2 - x

AbstractTemperature dependences of resistivity ρab(T) and ρc(T) of single-crystal films Nd2 − xCexCuO4 + δ (x = 0.12, 0.15, 0.17, 0.20) with orientations (001) and