Charge Imbalance and Crossed Andreev reflection in Py/Ta Devices

TL;DR

This paper investigates crossed Andreev reflection and charge imbalance in Py/Ta devices, revealing nonlocal conduction effects and their dependence on temperature and device geometry, advancing understanding of quantum entanglement in solid-state systems.

Contribution

It demonstrates the fabrication and measurement of Py/Ta devices showing nonlocal effects and charge imbalance, providing new insights into crossed Andreev reflection phenomena.

Findings

Observation of nonlocal conduction characteristic of crossed Andreev reflection.

Identification of charge imbalance effects near the superconducting transition temperature.

Dependence of nonlocal effects on device geometry and temperature.

Abstract

Crossed Andreev reflection in a lateral spin valve geometry device is an aspect of considerable recent interest, particularly with regards to Cooper pair splitting experiments to realize solid state quantum entanglement. In this work, devices are fabricated consisting of two ferromagnetic permalloy (Py) electrodes contacted by a overlaid perpendicular superconducting Ta electrode, of variable lateral in-plane offset within the expected BCS superconducting coherence length $\xi_0$. Experimental electrical transport measurements are presented of local and nonlocal conduction, showing characteristics of non-local or crossed Andreev reflection in the superconducting state at low temperatures in addition to nonlocal effects divergent for T$\rightarrow$T$_c$ attributed to nonlocal charge imbalance.