Speaker
Prof.
Nacho Pascual
(Ikerbasque Research Professor ,CIC nanogune)
Description
Magnetic impurities inside a superconductor locally distorts superconductivity. They scatter Cooper pairs as a potential with broken time-reversal symmetry, what leads to localized bound states (usually refered as Shiba states) with subgap excitation energies. These states, first predicted by Yu, Shiba, and Rusinov [1], are identified in scanning tunneling spectra as pairs of intra-gap resonances symmetrically positioned around zero-bias.
Most conventional approaches to study Shiba states treat magnetic impurities as point scatterers with an isotropic exchange interaction, while the complex internal structure of magnetic impurities is usually neglected. Due to the orbital character of the scattering channels of the impurities, it is expected that Shiba multiplets reflect the occupation level of the atomic shell, what would render them as the ideal probe for identifying the magnetic ground state of a single impurity in a superconductor.
In this presentation, I will show high-resolution scanning tunneling spectroscopy measurements and Density Functional Theory simulations, which provide evidence that that the number and shape of Shiba states are correlated to the spin-polarized atomic orbitals of the impurity, hybridized with the superconducting host. We investigated Cr impurities on Pb(111) [2] and spatially map the five Shiba excitations found inside the superconducting gap, resolving both their particle and hole components. While the maps of particle components resemble the d orbitals of embedded Cr atoms, the hole components differ strongly from them. The orbital fingerprints of Shiba states thus unveil the magnetic ground state of the impurity, and identify scattering channels and interactions, all valuable tools for designing atomic-scale superconducting devices.
Primary author
Prof.
Nacho Pascual
(Ikerbasque Research Professor ,CIC nanogune)
