Magnetic-Field-Induced Superconductivity in Ultrathin Pb Films with Magnetic Impurities

TL;DR

This study reveals that in ultrathin Pb films with magnetic impurities, applying a magnetic field can enhance superconductivity, contrary to typical suppression, due to effects like magnetic screening and Kondo singlet formation.

Contribution

It demonstrates that magnetic fields can induce or enhance superconductivity in ultrathin Pb films with magnetic impurities, a novel phenomenon not previously observed.

Findings

Magnetic field induces superconductivity in Ce-doped Pb films initially suppressed at zero field.

Screening of magnetic moments by conduction electrons affects the superconducting transition.

Capping with Au reduces magnetic screening, increasing the transition temperature under magnetic field.

Abstract

It is well known that external magnetic fields and magnetic moments of impurities both suppress superconductivity. Here, we demonstrate that their combined effect enhances the superconductivity of a few atomic layer thick Pb films grown on a cleaved GaAs(110) surface. A Ce-doped film, where superconductivity is totally suppressed at zero-field, actually turns superconducting when an external magnetic field is applied parallel to the conducting plane. For films with Mn adatoms, the screening of the magnetic moment by conduction electrons, i.e., the Kondo singlet formation, becomes important. We found that the degree of screening can be reduced by capping the Pb film with a Au layer, and observed the positive magnetic field dependence of the superconducting transition temperature.