Coherent versus Incoherent c-Axis Josephson Tunneling Between Layered Superconductors

TL;DR

This paper compares coherent and incoherent c-axis Josephson tunneling in layered superconductors, analyzing their effects on critical current and resistance, and discusses implications for experimental measurements in underdoped samples.

Contribution

It provides a detailed calculation of tunneling characteristics for both coherent and incoherent processes in layered superconductors, highlighting differences and experimental challenges.

Findings

Coherent tunneling occurs only for voltages below 2J/e.

Coherent critical current can be large and independent of the superconducting gap under certain conditions.

Measuring normal resistance Rn is difficult in underdoped samples due to voltage constraints.

Abstract

We calculate Ic(T) and Rn for both coherent and incoherent electron tunneling across a c-axis break junction between nu=s,d_x^2-y^2-wave superconducting half spaces, each with c-axis bandwidth 2J. Coherent quasiparticle tunneling only occurs for voltages V<2J/e, leading to difficulties in measuring Rn for underdoped samples. The coherent part of Ic(0) is independent of Delta_nu(0) for J/Delta_nu(0)<<1, and can be large. Our results are discussed with regard to recent experiments.