[{"type":"report","title":"Multi-atom quasiparticle scattering interference for superconductor energy-gap symmetry determination","issued":{"date-parts":[["2021","1","12"]]},"author":[{"family":"Sharma","given":"R."},{"family":"Kreisel","given":"A."},{"family":"Sulangi","given":"M. A."},{"family":"B\u00f6ker","given":"J."},{"family":"Kostin","given":"A."},{"family":"Allan","given":"M. P."},{"family":"Eisaki","given":"H."},{"family":"B\u00f6hmer","given":"Anna E."},{"family":"Canfield","given":"P. C."},{"family":"Eremin","given":"I."},{"family":"S\u00e9amus Davis","given":"J. C."},{"family":"Hirschfeld","given":"P. J."},{"family":"Sprau","given":"P. O."}],"abstract":"Complete theoretical understanding of the most complex superconductors requires a detailed knowledge of the symmetry of the superconducting energy-gap \u0394$\\frac{\u03b1}{k}$, for all momenta k on the Fermi surface of every band \u03b1. While there are a variety of techniques for determining |\u0394$\\frac{\u03b1}{k}$|, no general method existed to measure the signed values of \u0394$\\frac{\u03b1}{k}$. Recently, however, a technique based on phase-resolved visualization of superconducting quasiparticle interference (QPI) patterns, centered on a single non-magnetic impurity atom, was introduced. In principle, energy-resolved and phase-resolved Fourier analysis of these images identifies wavevectors connecting all k-space regions where \u0394$\\frac{\u03b1}{k}$ has the same or opposite sign. But use of a single isolated impurity atom, from whose precise location the spatial phase of the scattering interference pattern must be measured, is technically difficult. Here we introduce a generalization of this approach for use with multiple impurity atoms, and demonstrate its validity by comparing the \u0394$\\frac{\u03b1}{k}$ it generates to the \u0394$\\frac{\u03b1}{k}$ determined from single-atom scattering in FeSe where s\u00b1 energy-gap symmetry is established. Finally, to exemplify utility, we use the multi-atom technique on LiFeAs and find scattering interference between the hole-like and electron-like pockets as predicted for \u0394$\\frac{\u03b1}{k}$ of opposite sign.","kit-publication-id":"1000129377"}]