Hyperbolic Fringe Signal for Twin Impurity Quasiparticle Interference

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 (HFs) in the QPI signal can appear due to the loop contribution of the two-impurity scattering, where the locations of the two impurities are the hyperbolic focus points. For a single pocket Fermiology, a HF pattern signals chiral SC order for nonmagnetic impurities and requires magnetic impurities for a nonchiral SC. For a multipocket scenario, a sign-changing order parameter such as an s & PLUSMN; wave likewise yields a HF signature. We discuss twin impurity QPI as a new tool to complement the analysis of superconducting order from local spectroscopy.

Automated summary

We study the quasiparticle interference (QPI) pattern caused by adjacent impurities on the surface of a gapped superconductor (SC). We find that hyperbolic fringes (HFs) can appear in the QPI signal due to the loop contribution of two-impurity scattering, with the impurity locations as the hyperbolic focus points. For single pocket Fermiology, a HF pattern indicates chiral SC order with nonmagnetic impurities, and requires magnetic impurities for nonchiral SC. For multipocket scenario, a sign-changing order parameter like an s± wave also produces a HF signature. We discuss twin impurity QPI as a new tool to supplement the analysis of superconducting order from local spectroscopy.