Influence of magnetic impurities on charge transport in diffusive-normal-metal / superconductor junctions

TL;DR

This paper investigates how magnetic impurities in diffusive normal metals affect charge transport in superconductor junctions, revealing that impurity scattering suppresses the proximity effect and alters conductance depending on junction transparency and superconductor type.

Contribution

It provides a detailed analysis of magnetic impurity effects on charge transport in s- and d-wave superconductor junctions using Usadel equations, highlighting the contrasting impacts based on transparency.

Findings

Magnetic impurities suppress the proximity effect in all cases.

Zero-bias conductance is suppressed in low-transparent s-wave junctions.

In high-transparent junctions, magnetic impurities enhance zero-bias conductance.

Abstract

Charge transport in the diffusive normal metal (DN) / insulator / $s$- and $% d $-wave superconductor junctions is studied in the presence of magnetic impurities in DN in the framework of the quasiclassical Usadel equations with the generalized boundary conditions. The cases of $s$- and d-wave superconducting electrodes are considered. The junction conductance is calculated as a function of a bias voltage for various parameters of the DN metal: resistivity, Thouless energy, the magnetic impurity scattering rate and the transparency of the insulating barrier between DN and a superconductor. It is shown that the proximity effect is suppressed by magnetic impurity scattering in DN for any value of the barrier transparency. In low-transparent s-wave junctions this leads to the suppression of the normalized zero-bias conductance. In contrast to that, in high transparent junctions zero-bias conductance is enhanced by magnetic impurity scattering. The physical origin of this effect is discussed. For the d-wave junctions, the dependence on the misorientation angle $\alpha$ between the interface normal and the crystal axis of a superconductor is studied. The zero-bias conductance peak is suppressed by the magnetic impurity scattering only for low transparent junctions with $\alpha \sim 0$. In other cases the conductance of the d-wave junctions does not depend on the magnetic impurity scattering due to strong suppression of the proximity effect by the midgap Andreev resonant states.