Non-local Andreev reflection under ac bias

TL;DR

This paper provides a theoretical analysis of non-local electron transport in NSN devices under ac bias, revealing photon-assisted effects and conditions where crossed Andreev reflection dominates, leading to negative non-local conductance.

Contribution

It introduces a theoretical framework for understanding ac bias effects on non-local transport, highlighting photon-assisted violation of CAR and EC balance in NSN devices.

Findings

Non-local conductance can become negative at low frequencies and temperatures.

Photon-assisted processes can violate the balance between CAR and EC.

Predictions are testable in future experiments.

Abstract

We theoretically analyze non-local electron transport in multi-terminal normal-metal-superconductor-normal-metal (NSN) devices in the presence of an external ac voltage bias. Our analysis reveals a number of interesting effects, such as, e.g., photon-assisted violation of balance between crossed Andreev reflection (CAR) and elastic cotunneling (EC). We demonstrate that at sufficiently small (typically subgap) frequencies of an external ac signal and at low temperatures the non-local conductance of the NSN device turns negative implying that in this regime CAR contribution to the non-local current dominates over that of EC. Our predictions can be directly tested in future experiments.