Magnetic anisotropy in Shiba bound states across a quantum phase transition

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 tunnelling 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. Our results provide experimental insights into the phase diagram of a magnetic impurity on a superconducting host and shine light on the effects induced by magnetic anisotropy on many-body interactions.

Proximity-Induced Shiba States in a Molecular Junction

“…By virtue of a variable molecule-electrode coupling, we access both the singlet and doublet ground states of the hybrid system which give rise to the doublet and singlet Shiba excited states, respectively. Our results show that Shiba states are a robust feature of the interaction between a paramagnetic impurity and a proximity-induced superconductor where the excited state is mediated by correlated electron-hole (Andreev) A quantum dot (QD) or impurity coupled to a superconductor constitutes a rich physical system in which many-body effects compete for the ground state [1][2][3][4][5][6][7][8][9]. The ground state can take the form of a BCS-like singlet, a spin degenerate doublet, or a Kondo-like singlet, depending on the relative strengths of the characteristic energies of the competing phenomena (charging energy, U, superconducting gap, Δ, Kondo energy, k B T K ).…”

Spin-Resolved Spectroscopy of the Yu-Shiba-Rusinov States of Individual Atoms

“…DOI: 10.1103/PhysRevLett.119.197002 Recent investigations of chains [1][2][3] and arrays [4,5] of magnetic atoms in contact with surfaces of s-wave superconductors in view of Majorana zero modes and topological superconductivity triggered renewed interest in the properties of the basic constituent of such systems, the individual magnetic adatom. Typically, such adatoms induce quasiparticle excitations inside the superconducting energy gap [6][7][8], referred to as Yu-Shiba-Rusinov (YSR) states, which hamper the identification of topologically nontrivial edge states [3,9], calling for a thorough characterization of all experimentally accessible properties of YSR states.Following the first experimental verification of YSR states of individual atoms using scanning tunneling spectroscopy (STS) [10], there were numerous experimental studies, focusing on orbital effects [11][12][13], magnetic anisotropy [14], effects of reduced dimensionality of the superconductor [15], effects of coupling [11,16], and the competition between Kondo screening and superconducting pairing [17,18]. However, the investigation of the spin polarization of the YSR state of individual atoms, which could serve as a fingerprint for the distinction from topological states [19], was so far restricted to theoretical predictions [6][7][8][20][21][22].…”

“…Following the first experimental verification of YSR states of individual atoms using scanning tunneling spectroscopy (STS) [10], there were numerous experimental studies, focusing on orbital effects [11][12][13], magnetic anisotropy [14], effects of reduced dimensionality of the superconductor [15], effects of coupling [11,16], and the competition between Kondo screening and superconducting pairing [17,18]. However, the investigation of the spin polarization of the YSR state of individual atoms, which could serve as a fingerprint for the distinction from topological states [19], was so far restricted to theoretical predictions [6][7][8][20][21][22].…”

Topological superconductivity and anti-Shiba states in disordered chains of magnetic adatoms

“…In addition, variation of the exchange coupling J , originating from different microscopic coupling configurations between the atom and the substrate, will also translate into variation of α. Recently, this was employed in the observation of the ground state parity switching that takes place in a system with an isolated magnetic impurity at α = 1 [52]. We will allow α to vary locally as α i = α(1 + δα i ), where δα is a uniformly distributed with a finite bandwidth δα i ∈ [−ε,ε].…”