Enhancement of crossed Andreev reflection in a superconducting ladder connected to normal metal leads

TL;DR

This paper proposes a novel method to significantly enhance crossed Andreev reflection in a superconductor-normal metal setup by introducing a Josephson junction with phase control, enabling tunable transport regimes.

Contribution

It introduces a new scheme involving a Josephson junction to boost crossed Andreev reflection, overcoming previous limitations of competing electron tunneling.

Findings

Enhanced cAR achieved through phase-controlled Josephson junctions

Transition between ET and cAR regimes by tuning chemical potential

Presence of subgap Andreev states facilitating transport control

Abstract

Crossed Andreev reflection (cAR) is a scattering process that happens in a quantum transport set-up consisting of two normal metals (NM) attached to a superconductor (SC), where an electron incident from one NM results in a hole emerging in the other. Typically, an electron tunnelling through the superconductor from one NM to the other (ET) competes with cAR and masks the signature of cAR in the conductance spectrum. We propose a novel scheme to enhance cAR, in which SC part of the NM-SC-NM is side-coupled to another SC having a different SC phase to form a Josephson junction in the transverse direction. At strong enough coupling and adequate phase difference, one can smoothly traverse between highly ET-dominant to highly cAR-dominant transport regimes by tuning chemical potential, due to the appearance of subgap Andreev states that are extended in the longitudinal direction. We also discuss connections to realistic systems.