Multi-atom quasiparticle scattering interference for superconductor energy-gap symmetry determination

Sharma, R. and Kreisel, A. and Sulangi, M.A. and Böker, J. and Kostin, A. and Allan, M.P. and Eisaki, H. and Böhmer, A.E. and Canfield, P.C. and Eremin, I. and Séamus Davis, J.C. and Hirschfeld, P.J. and Sprau, P.O.

Volume: 6 Pages:
DOI: 10.1038/s41535-020-00303-4
Published: 2021

Complete theoretical understanding of the most complex superconductors requires a detailed knowledge of the symmetry of the superconducting energy-gap Δkα, for all momenta k on the Fermi surface of every band α. While there are a variety of techniques for determining ∣Δkα∣, no general method existed to measure the signed values of 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 all k-space regions where Δkα 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 Δkα it generates to the Δkα determined 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 Δkα of opposite sign. © 2021, Crown.

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