Anisotropy and spin-fluctuation effects on the spectral properties of Shiba impurities

DIPC Seminars

Alejandro M. Lobos
Instituto Interdisciplinario de Ciencias Básicas, Universidad Nacional de Cuyo - CONICET, Mendoza
Hybrid Seminar: Donostia International Physics Center
Miguel Angel Cazalilla
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Anisotropy and spin-fluctuation effects on the spectral properties of Shiba impurities

Magnetic impurities coupled to a superconductor substrate are interesting physical systems both from the fundamental perspective as well as for potential technological applications. In this work we theoretically consider a quantum magnetic impurity coupled to a superconductor, and obtain the local density of states at the position of the impurity. We take into account the effect of quantum fluctuations of the spin and the single-ion magnetic anisotropy. We particularly focus on the spectrum of subgap Yu-Shiba-Rusinov (YSR, or simply Shiba) states induced by a quantum impurity with easy- or hard-axis uniaxial anisotropy. Although this is a relevant experimental situation in, e.g., magnetic adatoms on the surface of clean metals, it is customary to assume a classical-spin approximation which is not able to capture single-ion anisotropy and other quantum effects. Here, by assuming the regime of weak- coupling, quantum fluctuations of the spin are taken into account in the equations of motion of the electronic Green’s function. We obtain important deviations with respect to the classical-spin approximation. Our results point towards the importance of incorporating quantum fluctuations and anisotropy effects for the correct interpretation of scanning tunneling microscopy (STM) experiments.