Intergrain Josephson Currents in Multigap Superconductors: Microscopic Origin of Low Intergrain Critical Current and Its Recovery Potential in Iron-Pnictide Materials

TL;DR

This paper investigates the microscopic origins of low intergrain Josephson currents in iron-pnictide superconductors, revealing how s-wave symmetry and incoherent tunneling suppress current and proposing ways to enhance it.

Contribution

It provides a microscopic theory explaining the low intergrain current in iron-pnictides and suggests strategies for its recovery based on tunneling and symmetry considerations.

Findings

Intergrain Josephson current is reduced by s-wave symmetry with incoherent tunneling.

Temperature dependence of the current is anomalously flat over a wide range.

Strategies for increasing intergrain current are proposed.

Abstract

We microscopically examine the intergrain Josephson current in iron-pnictide superconductors in order to solve the puzzle of why the intergrain current is much lower than the intragrain one. The theory predicts that the intergrain Josephson current is significantly reduced by the $\pm$s-wave symmetry when the incoherent tunneling becomes predominant and the density of states and the gap amplitude between two bands are identical. We find in such a situation that the temperature dependence of the intergrain Josephson current shows an anomalously flat curve over a wide temperature range. Finally, we suggest important points for increasing the intergrain current.