Zeeman effects on Yu-Shiba-Rusinov states

Abstract

When the exchange interaction between the impurity spin and the spins of itinerant quasiparticles are strong or weak enough, the ground states for a magnetic impurity in a superconductor are the screened or free spins, respectively. In both cases, the lowest excited state is a bound state within the superconducting gap, known as the Yu-Shiba-Rusinov (YSR) state. The YSR state is spatially localized, energetically isolated, and fully spin-polarized, leading to applications such as functional scanning probes. While any application demands identifying whether the impurity spin is screened or free, a suitable experimental technique has been elusive. Here we demonstrate an unambiguous way to determine the impurity ground state using the Zeeman effect. We performed ultra-low temperature scanning tunneling spectroscopy of junctions formed between a Cu(111) surface and superconducting Nb tips decorated by single magnetic Fe atoms. Depending on the condition of the Fe adsorbate, the YSR peak in the spectrum either splits or shifts in a magnetic field, signifying that the Fe spin is screened or free, respectively. Our observations provide renewed insights into the competition between magnetism and superconductivity and constitute a basis for the applications of the YSR state.

21 pages, 10 figures

References in corpus (7)

• Observation of Majorana Fermions in Ferromagnetic Atomic Chains on a Superconductor
• Fermi-liquid instabilities at magnetic quantum phase transitions
• Distinguishing a Majorana zero mode using spin resolved measurements
• Tuning Yu-Shiba-Rusinov States in a Quantum Dot
• Magnetic anisotropy effects on quantum impurities in superconducting host
• Scaling of Yu-Shiba-Rusinov energies in the weak-coupling Kondo regime
• Magnetic impurities in spin-split superconductors

Cited by in corpus (10)

• Tracking a Spin-Polarized Superconducting Bound State across a Quantum Phase Transition
• Phase shift and magnetic anisotropy induced field splitting of impurity states in (Li1-xFex)OHFeSe superconductor
• Searching for Majorana quasiparticles at vortex cores in iron-based superconductors
• Observation of Yu-Shiba-Rusinov-like states at the edge of CrBr3/NbSe2 heterostructure
• Theory of a Single Magnetic Impurity on a Thin Metal Film in Proximity to a Superconductor
• Magnetic bound states embedded in tantalum superconducting thin films
• Quantum spin driven Yu-Shiba-Rusinov multiplets and fermion-parity-preserving phase transition in K${}_3$C${}_{60}$
• Robust Spin Polarization of Yu-Shiba-Rusinov States in Superconductor/Ferromagnetic Insulator Heterostructures
• High-Resolution Spectroscopy of the Intermediate Impurity States near a Quantum Phase Transition
• Quantifying the quantum nature of high spin YSR excitations in transverse magnetic field