%ASharma, Rahul%AKreisel, Andreas%ASulangi, Miguel%ABöker, Jakob%AKostin, Andrey%AAllan, Milan%AEisaki, H.%ABöhmer, Anna%ACanfield, Paul%AEremin, Ilya%ASéamus Davis, J.%AHirschfeld, P.%ASprau, Peter%BJournal Name: npj Quantum Materials; Journal Volume: 6; Journal Issue: 1; Related Information: CHORUS Timestamp: 2022-12-02 17:38:32 %D2021%INature Publishing Group %JJournal Name: npj Quantum Materials; Journal Volume: 6; Journal Issue: 1; Related Information: CHORUS Timestamp: 2022-12-02 17:38:32 %K %MOSTI ID: 10209425 %PMedium: X %TMulti-atom quasiparticle scattering interference for superconductor energy-gap symmetry determination %XAbstract

Complete theoretical understanding of the most complex superconductors requires a detailed knowledge of the symmetry of the superconducting energy-gap$${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$Δkα, for all momentakon the Fermi surface of every bandα. While there are a variety of techniques for determining$$|{\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha |$$Δkα, no general method existed to measure the signed values of$${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$Δkα. 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 allk-space regions where$${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$Δkαhas 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$${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$Δkαit generates to the$${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$Δkαdetermined from single-atom scattering in FeSe where s±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$${\mathrm{{\Delta}}}_{\mathbf{k}}^\alpha$$Δkαof opposite sign.

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