Dynamical Shiba states by precessing magnetic moments in an s-wave superconductor

TL;DR

This paper theoretically investigates the dynamics of Shiba states around precessing magnetic moments in an s-wave superconductor, revealing how precession influences bound state energies, wavefunctions, and resulting charge and spin currents detectable via STM.

Contribution

It introduces a rotating wave approach to analyze the effects of magnetic moment precession on Shiba states and their associated currents, providing new insights into their dynamical behavior.

Findings

Precession modifies the Shiba bound state quasi-energy and spatial extent.

Charge and spin currents depend strongly on precession parameters and Shiba energy level.

The charge current reflects the electron-hole asymmetry of the Shiba state.

Abstract

We study theoretically the dynamics of a Shiba state forming around precessing classical spin in an s-wave superconductor. Utilizing a rotating wave description for the precessing magnetic impurity, we find the resulting Shiba bound state quasi-energy and the spatial extension of the Shiba wavefunction. We show that such a precession pertains to dc charge and spin currents flowing through a normal STM tip tunnel coupled to the superconductor in the vicinity of the impurity. We calculate these currents and find that they strongly depend on the magnetic impurity precession frequency, precession angle, and on the position of the Shiba energy level in the superconducting gap. The resulting charge current is found to be proportional to the difference between the electron and hole wavefunctions of the Shiba state, being a direct measure for such an asymmetry. By dynamically driving the impurity one can infer the spin dependence of the Shiba states in the absence of a spin-polarized STM tip