Lucas Schneider

Affiliation: University of California, Berkeley

Research Interests: Scanning Tunneling Microscopy, Superconductivity, Topology in Condensed Matter Physics, 2D Materials

Title: Superconductivity in atom-by-atom crafted quantum corrals

Abstract: Gapless materials in electronic contact with superconductors acquire proximity-induced superconductivity in a region near the interface. Here, we investigate the most miniature example of this so-called proximity effect on only a single quantum level of a surface state confined in a quantum corral on a superconducting substrate, built atom-by-atom using a scanning tunneling microscope. Whenever an eigenmode of the corral is pitched close to the Fermi energy by adjusting the corral’s size, a pair of very sharp particle-hole symmetric states is found to enter the superconductor’s gap. By comparison to a resonant level model of a spin-degenerate localized state coupled to a superconducting bath, we identify the in-gap states as scattering resonances theoretically predicted in 1972 which had so far eluded detection [1]. We further show that the observed anticrossings of the in-gap states indicate proximity-induced pairing in the quantum corral’s eigenmodes [2]. Based on these insights, I will discuss the implications on induced superconductivity in the surface state of noble metal Ag(111) grown on superconducting Nb(110). Notably, we find that the lifetime of electronic states is strongly enhanced by the presence of a proximity-induced bulk gap. Finally, we study how magnetic adatoms interact with the corral’s eigenmodes. Understanding their coupling eventually allows us to tailor a mirage effect [3] of Yu-Shiba-Rusinov sub-gap states induced by Fe atoms [4].