The estimation of coherence length for electron-doped superconductor Nd2−x_{2-x}Cex_xCuO4+δ_{4+\delta}

Results of low-temperature upper critical field measurements for Nd$_{2-x}$Ce$_x$CuO$_{4+\delta}$ single crystals with various $x$ and nonstoichiometric disorder ($\delta$) are presented. The coherence length of pair correlation $\xi$ and the product $k_F$$\xi$, where $k_F$ is the Fermi wave vector, are estimated. It is shown that for investigated single crystals parameter $k_F$$\xi$ $\cong$ 100 and thus phenomenologically NdCeCuO - system is in a range of Cooper-pair-based (BCS) superconductivity.Comment: 8 pages, 3 figures, 2 table

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

We present the investigation results of the in-plane \{rho}(T) resistivity tensor at the temperature range 0.4-40 K in magnetic fields up to 90kOe (H||c, J||ab) for electron-doped Nd{2-x}Ce{x}CuO{4+{\delta}} with different degree of disorder near antiferromagnetic - superconducting 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 (dHc2/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.Comment: 9 pages, 2 figure

Parabolic negative magnetoresistance in p-Ge/Ge1-xSix heterostructures

Quantum corrections to the conductivity due to the weak localization (WL) and the disorder-modified electron-electron interaction (EEI) are investigated for the high-mobility multilayer p-Ge/Ge1-xSix heterostructures at T = (0.1 - 20.0)K in magnetic field B up to 1.5T. Negative magnetoresistance with logarithmic dependence on T and linear in B^2 is observed for B >= 0.1T. Such a behavior is attributed to the interplay of the classical cyclotron motion and the EEI effect. The Hartree part of the interaction constant is estimated (F_/sigma = 0.44) and the WL and EEI contributions to the total quantum correction /Delta /sigma at B = 0 are separated (/Delta /sigma_{WL} ~ 0.3/Delta /sigma; /Delta /sigma_{EEI} ~ 0.7/Delta /sigma).Comment: 3 pages, 4 figure

Two-dimensional quantum interference contributions to the magnetoresistance of Nd{2-x}Ce{x}CuO{4-d} single crystals

The 2D weak localization effects at low temperatures T = (0.2-4.2)K have been investigated in nonsuperconducting sample Nd{1.88}Ce{0.12}CuO{4-d} and in the normal state of the superconducting sample Nd{1.82}Ce{0.18}CuO{4-d} for B>B_c2. The phase coherence time and the effective thickness $d$ of a conducting CuO_2 layer have been estimated by the fitting of 2D weak localization theory expressions to the magnetoresistivity data for the normal to plane and the in-plane magnetic fields.Comment: 5 pages, 4 postscript figure