Magnetic field dependence of magnetic impurities on superconductors

Abstract

Magnetic adatoms can be considered as impurities that weaken the binding of superconducting Cooper pairs leading to impurity levels in the gap: so-called Yu-Shiba-Rusinov (YSR) states. In-gap states caused by a Cr magnetic impurity on a superconducting Pb (111) thin film are studied in the presence of an external magnetic field using a scanning tunneling microscope. We show that the lifetimes of these states can be considerably modified by applying magnetic fields. The result shows that the magnetic impurity does not alter the superconducting gap however, it enhances the rate of Cooper-pair dissociation by a constant value. Surprisingly, the large Pb spin-orbit coupling does not influence the field-induced depairing and we show that only orbital effects intervene in the effective destruction of Pb superconductivity by an external magnetic field.