Transport properties of Nd 2−x Ce x CuO 4+δ single crystal films (B c, J ab) are investigated in magnetic fields B up to 9T at T =(0.4-4.2)K. An analysis of normal state (at B > B c2 ) Hall coefficient R H n dependence on Ce doping takes us to a conclusion about the existence both of electron-like and hole-like contributions to transport in nominally electron-doped system. In accordance with R H n (x) analysis an anomalous sign reversal of Hall effect in mixed state at B < B c2may be ascribed to a flux-flow regime for two types of carriers with opposite charges.
We present the investigation results of the in-plane ρ(T) resistivity tensor at the temperature range 0.4-40 K in magnetic fields up to 90kOe (H c, J ab) for electrondoped Nd 2−x Ce x CuO 4+δ with different degree of disorder near antiferromagneticsuperconducting phase boundary. We have experimentally found that for optimally doped compound both the upper critical field slope and the critical temperature decrease with increasing of the disorder parameter (d-wave pairing) while in the case of the underdoped system the critical temperature remains constant and (dH c2 /dT )| Tc increases with increasing of the disorder (s-wave pairing). These features suggest a possible implementation of the complex mixture state as the (s+id)-pairing.
The magnetic-field dependencies of the longitudinal and Hall resistance of the electron-doped compounds Nd 2−x Ce x CuO 4+δ in underdoped region with x = 0.14 and with varying degrees of disorder (δ) were investigated. It was established experimentally that the correlation between the longitudinal electrical resistivity and the Hall resistivity can be analyzed on the basis of scaling relationships: ρ xy (B)∼ ρ β xx (B). For the totality of the investigated single-crystal films of Nd 2−x Ce x CuO 4+δ /SrTiO 3 the universal value β = 1.5 ±0.4 is found. The observed feature in the electron-doped two-dimensional systems can be associated both with a displaying of anisotropic s -wave or d-wave pairing symmetry and with a rather strong pinning due to an essential degree of disorder in the samples under study.
We present resistivity measurements of the upper critical field (H c2 ) phase diagram as a function of temperature (T) for Nd 1.85 Ce 0.15 CuO 4+δ /SrTiO 3 single crystal films with different degree of disorder (δ) in magnetic fields up to 90 kOe at temperatures down to 0.4 K. The data are well described by a two-band/two-gap model for a superconductor in the dirty limit.
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.
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