Theory of enhanced proximity effect by mid gap Andreev resonant state in diffusive normal metal / triplet superconductor junctions

TL;DR

This paper investigates how mid gap Andreev resonant states enhance the proximity effect in diffusive normal metal/triplet superconductor junctions, revealing conductance features and proposing tests for triplet pairing identification.

Contribution

It introduces a theoretical analysis of the proximity effect enhancement due to MARS in DN/TS junctions using Green's function formalism, focusing on p-wave superconductors.

Findings

Zero bias conductance peak (ZBCP) observed in conductance spectra.

Zero energy peak (ZEP) in local density of states (LDOS).

Suppression of peaks by magnetic field.

Abstract

Enhanced proximity effect by mid gap Andreev resonant state (MARS) in a diffusive normal metal / insulator / triplet superconductor (DN/TS) junction is studied based on the Keldysh-Nambu quasiclassical Green's function formalism. By choosing a p-wave superconductor as a typical example of TS, conductance of the junction and the spatial variation of quasiparticle local density of states (LDOS) in DN are calculated as the function of the magnitudes of the resistance $R_{d}$, Thouless energy in DN and the transparency of the insulating barrier. The resulting conductance spectrum has a zero bias conductance peak (ZBCP) and LDOS has a zero energy peak (ZEP) except for $\alpha = \pi/2$ $(0 \leq \alpha \leq \pi/2)$, where $\alpha$ denotes the angle between the lobe direction of the p-wave pair potential to the normal to the interface. These peaks are revealed to be suppressed by applying a magnetic field. When the magnitude of $R_{d}/R_{0}$ is sufficiently large, the total zero voltage resistance of the junction is almost independent of the $R_{d}$ for $\alpha \neq \pi/2$. The extreme case is $\alpha=0$, where total zero voltage resistance is always $R_{0}/2$. Based on these results, a crucial test to identify triplet pairing superconductors based on tunneling experiments is proposed.