Tunable crossed Andreev reflection in a heterostructure consisting of ferromagnets, normal metal and superconductors

TL;DR

This paper proposes a tunable heterostructure setup with ferromagnets, normal metals, and superconductors that allows control over crossed Andreev reflection probabilities via gate voltage, enabling adjustable nonlocal transport phenomena.

Contribution

The study introduces a novel, gate-tunable heterostructure configuration that enables dynamic control of crossed Andreev reflection and electron reflection probabilities.

Findings

CAR probability can be tuned from 0 to 1.

Differential transconductance can be adjusted from 0 to -e^2/h.

The setup demonstrates control over nonlocal transport phenomena.

Abstract

Crossed Andreev reflection (CAR) is a nonlocal transport phenomenon in a system of two normal metal (NM) leads connected to a superconductor (SC) that converts the electron like excitations in one metallic lead into hole like excitations in the other metallic lead. The scattering phenomena viz. electron tunneling (ET), electron reflection (ER) and Andreev reflection (AR) compete with CAR and reduce the probability of CAR generically. One of the experimentally realized proposals to observe CAR is to employ two ferromagnetic (FM) leads in antiparallel configuration connected to the SC by suppressing ET and AR. But CAR probability cannot be tuned in this setup. We propose a setup consisting of a gate tunable NM region connected to two superconducting regions on either side which are connected to FM leads further away in antiparallel configuration, in which probabilities of CAR and ER can be changed from $0$ to $1$ by a changing the gate voltage applied to the NM region. The gate voltage applied to the NM region dictates the chemical potential of the NM region and gives a handle on the Fabry-P\'erot interference of the electron and hole modes in the NM region. We calculate differential transconductance for the proposed setup which can be tuned across the range $0$ to $-e^2/h$.