ARPES Detection of Superconducting Gap Sign in Unconventional Superconductors

TL;DR

This paper introduces a novel ARPES-based method to directly detect the sign of the superconducting gap in unconventional superconductors, enhancing the understanding of their pairing mechanisms.

Contribution

It proposes a new ARPES technique to measure the superconducting gap sign, validated in cuprates, applicable to multiband superconductors like iron-based ones.

Findings

Successfully validated in cuprate superconductor

Sensitive to relative gap sign between bands

Applicable to multiorbital superconductors

Abstract

Superconductivity is realized by opening a gap in the superconducting state. The gap symmetry is crucial in understanding the underlying superconductivity mechanism. The magnitude and the phase are essential in fully characterizing the superconducting gap. Angle-resolved photoemission spectroscopy (ARPES) has played a key role in determining the gap symmetry in unconventional superconductors. However, it has been considered so far that ARPES can only measure the magnitude of the superconducting gap but not its phase; the phase has to be detected by other phase-sensitive techniques. Here we propose a new method to directly detect the superconducting gap sign by using ARPES. This method is successfully validated in a cuprate superconductor with a well-known $d$-wave gap symmetry. When two bands are nearby in momentum space and have a strong interband interaction, the resulted electronic structures in the superconducting state are sensitive to the relative gap sign between the two bands which can be captured by ARPES measurements. Our present work provides a new way to detect the gap sign and can be applied to various superconductors, particularly those with multiple orbitals like the iron-based superconductors. It also makes ARPES more powerful to determine both the gap magnitude and the phase that are significant in understanding the superconductivity mechanism of unconventional superconductors.