Mapping the orbital structure of impurity bound states in a superconductor
Deung Jang Choi (CIC NanoGUNE)
Carmen Rubio-Verdú (CIC NanoGUNE)
J. De Bruijckere (Kavli institute of nanoscience Delft, TU Delft - QN/van der Zant Lab, CIC NanoGUNE)
Miguel M. Ugeda (CIC NanoGUNE, Basque Foundation for Science)
Nicolas Lorente (Centro Mixto CSIC-UPV/EHU, Donostia International Physics Center)
Jose Ignacio Pascual (CIC NanoGUNE, Basque Foundation for Science)
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Abstract
A magnetic atom inside a superconductor locally distorts superconductivity. It scatters Cooper pairs as a potential with broken time-reversal symmetry, leading to localized bound states with subgap excitation energies, named Shiba states. Most conventional approaches regarding Shiba states treat magnetic impurities as point scatterers with isotropic exchange interaction. Here, we show that the number and the shape of Shiba states are correlated to the spin-polarized atomic orbitals of the impurity, hybridized with the superconductor. Using scanning tunnelling spectroscopy, we spatially map the five Shiba excitations found on subsurface chromium atoms in Pb(111), resolving their particle and hole components. While particle components resemble d orbitals of embedded Cr atoms, hole components differ strongly from them. Density functional theory simulations correlate the orbital shapes to the magnetic ground state of the atom, and identify scattering channels and interactions, all valuable tools for designing atomic-scale superconducting devices.
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