Tracking a Spin-Polarized Superconducting Bound State across a Quantum Phase Transition

Abstract

The magnetic exchange coupling between magnetic impurities and a superconductor induce so-called Yu-Shiba-Rusinov (YSR) states which undergo a quantum phase transition (QPT) upon increasing the exchange interaction beyond a critical value. While the evolution through the QPT is readily observable, in particular if the YSR state features an electron-hole asymmetry, the concomitant change in the ground state is more difficult to identify. We use ultralow temperature scanning tunneling microscopy to demonstrate how the change in the YSR ground state across the QPT can be directly observed for a spin-1/2 impurity in a magnetic field. We observe a change in the excitation spectrum from the doublet ground state in the free spin regime (two spectral features) to the singlet ground state in the screened spin regime (four spectral features). We also identify a transition regime, where the YSR excitation energy is smaller than the Zeeman energy. We thus provide a straightforward way for unambiguously identifying the ground state of a spin-1/2 YSR state.

arXiv comment11 pages, 10 figures, including supplementary information

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Cited by in corpus (6)

• Nanoscale Control of Quantum States in Radical Molecules on Superconducting Pb(111)
• Observation of Yu-Shiba-Rusinov-like states at the edge of CrBr3/NbSe2 heterostructure
• 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
• Spatially Dependent in-Gap States Induced by Andreev Tunneling through a Single Electronic State
• Spin-resolved nonlocal transport in proximitized Rashba nanowires