Resistivity tensor correlations in the mixed state of electron-doped superconductor Nd2−xCe x CuO4+δ

Abstract

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.

Fe–As Bond Fluctuations in a Double-Well Potential in LaFeAsO

“…Here we report the analysis of polarized As K-edge extended x-ray-absorption finestructure (EXAFS) measurements of undoped and cobalt doped LaFeAsO performed to unveil the local fast Fe-As zero point fluctuations in a double-well potential. This approach was successfully applied to hole doped cuprates [24][25][26][27], Ba 1-x K x BiO 3 and electron doped cuprates [28][29][30]. Polarized As K-edge EXAFS in 1111 systems gives instantaneous pair distribution function between As and neighboring Fe atoms.…”

Hall Resistivity Correlations in Disordered Electron-Doped $$\hbox {Nd}_{2-x}\hbox {Ce}_x\hbox {CuO}_{4+\delta }$$ Nd 2 - x

“…1a. In the mixed state the longitudinal and Hall resistivities there are the resistivity correlations ρ xy (B)∼ [ρ xx (B)] β that was found for different kinds of HTSC (see references in [15]). The log-log plot for Nd 1.85 Ce 0.15 CuO 4+δ /SrTiO 3 films with different disorder parameters k F ℓ at T = 4.2K (Fig.…”

“…As a result, three types of samples with x=0.15 were obtained: "as grown" samples, "optimally reduced" -after annealing in a vacuum and "non optimally reduced" samples [14]. For films with x = 0.14 were obtained two types of samples: "optimally reduced" and two samples "non optimally reduced" -non optimally annealed in vacuum [14,15]. The thickness of the films was d = 1600-3800Å.…”

“…Our previous investigations point out that the change in the oxygen concentration leads to a change in the degree of nonstoichiometric disorder [6,7,8,15]. Annealing in an oxygen-free atmosphere leads to a change in impurity scattering, while having little effect on the concentration of charge carriers and we will use the concepts of the theory of random two-dimensional systems where the parameter k F ℓ serves as the measure of disorder in the system.…”

“…The magnetic field dependencies of ρ xx (B) and ρ xy (B) of underdoped (x = 0.14) superconductor Nd 2−x Ce x CuO 4+δ with varying k F ℓ at T = 4.2 K were investigated and presented in [15]. As in the case of the optimally doped compounds we see the increase of the index β with increase of the disorder (k F ℓ decreases) from β = 1.11 ± 0.01 up to β = 1.21 ± 0.01 for the film with k F ℓ = 6.0 and β = 1.17 ± 0.03 for the film with k F ℓ = 2.3.…”