Spin Inelastic Electron Tunneling Spectroscopy on Local Magnetic Moment Embedded in Josephson Junction

TL;DR

This paper theoretically investigates spin inelastic electron tunneling spectroscopy on local magnetic moments embedded in Josephson junctions, revealing how superconducting gaps influence excitation signatures and how magnetic fields can resolve degeneracies.

Contribution

It provides a theoretical framework explaining experimental conductance features in superconducting STM measurements of magnetic adsorbates, including the effects of superconducting gaps and magnetic field splitting.

Findings

Excitations occur only above the combined superconducting gap and spin excitation energies.

Additional current signatures arise from pumping into higher spin states.

External magnetic fields can resolve degeneracies by Zeeman splitting.

Abstract

Recent experimental conductance measurements performed on paramagnetic molecular adsorbates on a superconducting surface, using superconducting scanning tunneling microscopy techniques, are theoretically investigated. For low temperatures, we demonstrate that tunneling current assisted excitations of the local magnetic moment cannot occur for voltage biases smaller than the superconducting gap of the scanning tunneling microscope. The magnetic moment is only excited for voltages corresponding to the sum of the superconducting gap and the spin excitation energies. In excellent agreement with experiment, we show that pumping into higher excitations give additional current signatures by accumulation of density in the lower ones. Using external magnetic fields, we Zeeman split possible degeneracy and thereby resolve all excitations comprised in the magnetic moment.