Andreev-Bragg reflection from an Amperian superconductor

TL;DR

This paper proposes an electrical measurement method to detect Amperian pairing in high-$T_c$ cuprates via Andreev-Bragg reflections, which produce distinctive momentum shifts detectable in a three-terminal device.

Contribution

It introduces a novel electrical detection technique for Amperian pairing using Bragg scattering effects in a three-terminal setup.

Findings

Cross-conductance sign reverses for Amperian pairing

Bragg scattering causes odd multiples of $2k_F$ momentum shifts

Method distinguishes Amperian pairing from BCS and normal states

Abstract

We show how an electrical measurement can detect the pairing of electrons on the same side of the Fermi surface (Amperian pairing), recently proposed by Patrick Lee for the pseudogap phase of high-$T_c$ cuprate superconductors. Bragg scattering from the pair-density wave introduces odd multiples of $2k_{\rm F}$ momentum shifts when an electron incident from a normal metal is Andreev-reflected as a hole. These Andreev-Bragg reflections can be detected in a three-terminal device, containing a ballistic Y-junction between normal leads $(1,2)$ and the superconductor. The cross-conductance $dI_1/dV_2$ has the opposite sign for Amperian pairing than it has either in the normal state or for the usual BCS pairing.