Fresnel aperture diffraction: a phase-sensitive probe for superconducting pairing symmetry

TL;DR

This paper proposes a phase-sensitive diffraction technique using Fresnel aperture diffraction to determine the pairing symmetry and Fermi surface characteristics of superconductors, especially applicable to complex multi-band systems like iron-based superconductors.

Contribution

It introduces FSAD as a novel method to probe superconducting pairing symmetry and Fermi surface features with phase sensitivity.

Findings

FSAD pattern minima indicate even pairing symmetry.

FSAD pattern maxima indicate odd pairing symmetry.

Method applicable to complex multi-band superconductors like iron-based ones.

Abstract

Fresnel single aperture diffraction (FSAD) is proposed as a phase-sensitive probe for pairing symmetry and Fermi surface of a superconductor. We consider electrons injected, through a small aperture, into a thin superconducting (SC) layer. It is shown that in case of SC gap symmetry $\Delta(-k_x,\mathbf{k}_\parallel)=\Delta(k_x,\mathbf{k}_\parallel)$ with $k_x$ and $\mathbf{k}_\parallel$ respectively the normal and parallel component of electron Fermi wavevector, quasiparticle FSAD pattern developed at the image plane is zeroth-order minimum if $k_x x=n\pi$ ($n$ is an integer and $x$ is SC layer thickness). In contrast, if $\Delta(-k_x,\mathbf{k}_\parallel)=-\Delta(k_x, \mathbf{k}_\parallel)$, the corresponding FSAD pattern is zeroth-order maximum. Observable consequences are discussed for iron-based superconductors of complex multi-band pairings.