Super-Andreev reflection and longitudinal shift of pseudospin-one fermions

TL;DR

This paper explores the unique Andreev reflection properties of pseudospin-1 fermions, revealing a super-Andreev effect with perfect interface transparency and forward longitudinal shifts, which could be experimentally observed.

Contribution

It uncovers the super-Andreev reflection phenomenon in pseudospin-1 fermions, demonstrating enhanced and tunable Andreev reflection efficiency unlike previous models.

Findings

Pseudospin-1 fermions exhibit near-perfect Andreev reflection for all incident angles.

The super-Andreev reflection leads to high interface transparency and conductance peaks.

Longitudinal shifts are always forward in the subgap regime, regardless of reflection type.

Abstract

Novel fermions with a pseudospin-1 structure can be realized as emergent quasiparticles in condensed matter systems. Here, we investigate its unusual properties during the Andreev reflection at a normal-metal/superconductor (NS) interface. We show that distinct from the previously studied pseudospin-1/2 and two dimensional electron gas models, the pseudospin-1 fermions exhibit a strongly enhanced Andreev reflection probability, and remarkably, can be further tuned to approach perfect Andreev reflection with unit efficiency for all incident angles, exhibiting a previously unknown {super-Andreev reflection effect}. The super-Andreev reflection leads to perfect transparency of the NS interface that strongly promotes charge injection into the superconductor, and directly manifests as a differential conductance peak which can be readily probed in experiment. Additionally, we find that sizable longitudinal shifts exist in the normal and Andreev reflections of pseudospin-1 fermions. Distinct from the pseudospin-1/2 case, the shift is always in the forward direction in the subgap regime, regardless of whether the reflection is of retro- or specular type.