T. B. Charikova

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

Upper Critical Field in Electron-Doped Superconductor with Nonstoichiometric Disorder near Antiferromagnetic-Superconducting Phase Boundary

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Doping effect on the evolution of the pairing symmetry in n-type superconductor near antiferromagnetic phase boundary

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.

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

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.

Pairing type change upon an increase in the cerium doping level in the Nd2 − xCexCuO4 + δ electronic superconductor

Using the resistivity method it was found that temperature dependence of the upper critical field for underdoped Nd1.86Ce0.14CuO4+δ have an anomalous upward curvature of Hc2(T) dependence and can be consistently explained by the two-band/two-gap model of a dirty superconductor. Near antiferromagnetic-superconducting phase boundary the critical temperature remains constant with the change of the disorder parameter and the slope of Bc2 increases with increasing of the disorder parameter. This behavior is completely different from dependencies for pure superconducting phase at optimal doping region. This difference may indicate the change of the type of the paring: from the predominance of the anisotropic s-wave component (may be due to unstable competition between antiferromagnetic (AF) and superconducting (SC) regions) in underdoped (x=0.14) region to the prevalence of d-wave part in optimal doped regions (x=0.15) because of residual spin fluctuations.

Anomalous Hall effect in electron-doped Nd2−xCexCuO4+δ superconductor with nonstoichiometric disorder

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

Correlation between the Hall Resistance and Magnetoresistance in the Mixed State of an Nd2 − xCexCuO4 + δ Electronic Superconductor

(dB_{c2} /dT)_{T \to T_c }