Quantum spin driven Yu-Shiba-Rusinov multiplets and fermion-parity-preserving phase transition in K${}_3$C${}_{60}$

Abstract

Magnetic impurities in superconductors are of increasing interest due to emergent Yu-Shiba-Rusinov (YSR) states and Majorana zero modes for fault-tolerant quantum computation. However, a direct relationship between the YSR multiple states and magnetic anisotropy splitting of quantum impurity spins remains poorly characterized. By using scanning tunneling microscopy, we resolve systematically individual transition-metal (Fe, Cr and Ni) impurities induced YSR multiplets as well as their Zeeman effects in K${}_3$C${}_{60}$ superconductor. The YSR multiplets show identical $d$ orbital-like wave functions that are symmetry-mismatched to the threefold K${}_3$C${}_{60}$(111) host surface, breaking point-group symmetries of the spatial distribution of YSR bound states in real space. Remarkably, we identify an unprecedented fermion-parity-preserving quantum phase transition between ground states with opposite signs of the uniaxial magnetic anisotropy that can be manipulated by an external magnetic field. These findings can be readily understood in terms of anisotropy splitting of quantum impurity spins, and thus elucidate the intricate interplay between the magnetic anisotropy and YSR multiplets.

arXiv comment38 pages, 4 figures in the main text

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Cited by in corpus (4)

• Majorana quasiparticles in atomic spin chains on superconductors
• Double-quantum-dot Andreev molecules: Phase diagrams and critical evaluation of effective models
• Magnetic bound states embedded in tantalum superconducting thin films
• Quantifying the quantum nature of high spin YSR excitations in transverse magnetic field