Magnetic anisotropy in Shiba bound states across a quantum phase transition

TL;DR

This study uses scanning tunneling spectroscopy to investigate magnetic anisotropy effects on Shiba states in Manganese phthalocyanine molecules on Pb(111), revealing how anisotropy influences quantum ground states.

Contribution

It provides direct experimental evidence of magnetic anisotropy effects on Shiba states and clarifies the nature of quantum ground states in magnetic adatoms on superconductors.

Findings

Observation of triplet-split Shiba states due to anisotropy

Spectral weight analysis confirms ground state nature

Identification of quantum phase transition signatures

Abstract

The exchange coupling between magnetic adsorbates and a superconducting substrate leads to Shiba states inside the superconducting energy gap and a Kondo resonance outside the gap. The exchange coupling strength determines whether the quantum many-body ground state is a Kondo singlet or a singlet of the paired superconducting quasiparticles. Here, we use scanning tunneling spectroscopy to identify the different quantum ground states of Manganese phthalocyanine on Pb(111). We observe Shiba states, which are split into triplets by magnetocrystalline anisotropy. Their characteristic spectral weight yields an unambiguous proof of the nature of the quantum ground state.