Charge Transport in Junctions between D-Wave Superconductors

TL;DR

This paper provides a microscopic analysis of charge transport in d-wave superconductor junctions, revealing effects of crystal orientation on the Josephson current, nonharmonic current-phase relations, and low-temperature I-V anomalies relevant to high-temperature superconductors.

Contribution

It introduces a detailed microscopic model for d-wave superconductor junctions, highlighting orientation-dependent effects and novel features of current-phase relations and I-V characteristics.

Findings

Superconducting order parameter can be suppressed near boundaries depending on orientation.

The Josephson current exhibits a crossover behavior near the critical temperature.

Low-temperature I-V curves show distinct zero-bias anomalies depending on junction type.

Abstract

We develop a microscopic analysis of superconducting and dissipative currents in junctions between superconductors with d-wave symmetry of the order parameter. We study the proximity effect in such superconductors and show that for certain crystal orientations the superconducting order parameter can be essentially suppressed in the vicinity of a nontransparent specularly reflecting boundary. This effect strongly influences the value and the angular dependence of the dc Josephson current $j_S$. At $T \sim T_c $ it leads to a crossover between $j_S \propto T_c-T$ and $j_S \propto (T_c-T)^2$ respectively for homogeneous and nonhomogeneous distribution of the order parameter in the vicinity of a tunnel junction. We show that at low temperatures the current-phase relation $j_S(\varphi )$ for SNS junctions and short weak links between d-wave superconductors is essentially nonharmonic and contains a discontinuity at $\varphi =0$. This leads to further interesting features of such systems which can be used for novel pairing symmetry tests in high temperature superconductors (HTSC). We also investigated the low temperature I-V curves of NS and SS tunnel junctions and demonstrated that depending on the junction type and crystal orientation these curves show zero-bias anomalies $I\propto V^2$, $I\propto V^2\ln (1/V)$ and $I\propto V^3$ caused by the gapless behavior of the order parameter in d-wave superconductors. Many of our results agree well with recent experimental findings for HTSC compounds.