We study the quasiparticle interference (QPI) pattern emanating from a pair of adjacent impurities on the surface of a gapped superconductor (SC). We find that hyperbolic fringes (HF) in the QPI signal can appear due to the loop contribution of the two-impurity scattering, where the location of the two impurities are the hyperbolic focus points. For a single pocket Fermiology, an HF pattern signals chiral SC order for non-magnetic impurities and requires magnetic impurities for non-chiral SC. For a multi-pocket scenario, a sign-changing order parameter such as s±-wave likewise yields an HF signature. We discuss twin impurity QPI as a new tool to complement the analysis of superconducting order from local spectroscopy.
Cite
@article{arxiv.2207.01774,
title = {Hyperbolic fringe signal for twin impurity quasiparticle interference},
author = {Peize Ding and Tilman Schwemmer and Ching Hua Lee and Xianxin Wu and Ronny Thomale},
journal= {arXiv preprint arXiv:2207.01774},
year = {2023}
}