G. I. Kharus

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 the nonstoichiometric disorder on the temperature dependence of the upper critical field in Nd2−xCexCuO4+δ electron superconductors

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

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.

Effects of d-wave pairing in n-type high-temperature superconductors with anisotropic impurity scattering

Magnetoresistance in n-InxGa1−xAs/GaAs (x ≈ 0.18) heterostructures with double quantum wells (DQWs) was studied in the magnetic field parallel to the DQW layer. Specific features of the magnetoresistance, related to the passing of the tunnel gap edges across the Fermi level, are revealed and studied. Agreement between the calculated and experimental positions of the observed features is obtained when the spin splitting of the energy spectrum is taken into account. Earlier, similar features were observed in the magnetoresistance of n-GaAs/AlxGa1−xAs DQW heterostructures, but the spin effects did not manifest themselves.

Evaluation of mobility gaps and density of localized hole states in p-Ge/Ge1−xSix heterostructures in the quantum Hall effect mode

The temperature dependences of the resistance of the Nd2−xCexCuO4+δ single crystal with x = 0.15 and various disorder parameters δ have been investigated in various magnetic fields (B ‖ c, J ‖ ab) in the temperature range T = 1.8–40 K. It has been shown that the slope of the upper critical field, (dBc2/dT)|Tc, in the electron superconductor decreases with an increase in the disorder parameter. This dependence makes it possible to experimentally distinguish between d-pairing superconductors and s-pairing superconductors. The dependence of the superconducting transition temperature on the disorder parameter in the system is investigated in the model of the superconductors with anisotropic impurity scattering.

Shubnikov-de Haas oscillations in HgSe〈Fe〉 and HgSe〈Co〉 under hydrostatic pressure

The longitudinal ρxx(B) and Hall ρxy(B) magnetoresistances are investigated experimentally in the integer quantum Hall effect (QHE) regime in n-InGaAs/GaAs double quantum well nanostructures in the range of magnetic fields B = (0–16) T and temperatures T = (0.05–70) K before and after IR illumination. The results are evaluated within the scaling hypothesis with regard to electron-electron interaction.

Temperature dependence of the bandwidth of delocalized states for n-InGaAs/GaAs in the quantum Hall effect regime

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.

Magnetoresistance and hall effect in electron-doped superconductor Nd2 − xCexCuO4+δ with different degrees of nonstoichiometric disorder: A two-band model

AbstractThe temperature dependences of the resistivity of single-crystal films of the Nd2 − xCexCuO4 + δn-type superconductors with x = 0.14 (underdoped region) and x = 0.15 (optimal doping region) and different degrees of disorder δ have been investigated in various magnetic fields (B ‖ c, J ‖ ab) in the temperature range 0.4–300 K. It has been demonstrated that there are differences in the behavior of the dependences of the slope of the upper critical field