Correlation of Yu–Shiba–Rusinov States and Kondo Resonances in Artificial Spin Arrays on an s-Wave Superconductor

Abstract

Mutually interacting magnetic atoms coupled to a superconductor have gained enormous interest due to their potential for the realization of topological superconductivity. Individual magnetic impurities produce states within the superconducting energy gap known as Yu–Shiba–Rusinov (YSR) states. Here, using the tip of a scanning tunneling microscope, we artificially craft spin arrays consisting of an Fe adatom interacting with an assembly of interstitial Fe atoms (IFA) on a superconducting oxygen-reconstructed Ta(100) surface and show that the magnetic interaction between the adatom and the IFA assembly can be tuned by adjusting the number of IFAs in the assembly. The YSR state experiences a characteristic crossover in its energetic position and particle–hole spectral weight asymmetry when the Kondo resonance shows spectral depletion around the Fermi energy. By the help of slave-boson mean-field theory (SBMFT) and numerical renormalization group (NRG) calculations we associate the crossover with the transition from decoupled Kondo singlets to an antiferromagnetic ground state of the Fe adatom spin and the IFA assembly effective spin.

Spin-dependent resonant Andreev tunneling in hybrid ferromagnetic metal - magnetic quantum dot - superconductor nanostructures

“…The nanoparticles having a nonzero magnetic moment break time-reversal symmetry as well as spinrotation symmetry and can create topologically protected quasiparticle's bound states in proximity induced triplet superconducting gap [2 -7]. Individual magnetic impurities can also produce states inside the superconducting energy gap known as Yu-Shiba-Rusinov states [26,28] (see also [29] and references therein). Whether the experimentally observed ZBCPs in superconducting hybrid structures arise due to MZMs or not remains a key question because the nanoparticles disorder can also result in spurious zero-bias anomalies.…”

“…Yet, the presence of a smooth varying spin-dependent potential background in the nanowire (e.g., paramagnetic impurities) could produce, in some situations, trivial ZBCPs in tunneling measurements mimicking ones induced by MZMs [26][27][28][29]. In a tunneling spectra of confined normal metal-SC systems the Andreev bound state (ABS) can accidentally localized at a SC gap mid and thus the origin of the related conductance peak can falsely be interpreted in terms of a topological Majorana state.…”

Shiba states in systems with density of states singularities

“…If the nontrivial topological phase is realized [35], the Majorana end modes can occur [36]. Recently this type of structures were realized in many experiments [37][38][39][40][41][42][43].…”

The $\mathbf{Z}_{2}$ topological invariants in 2D and 3D topological superconductors without time reversal symmetry

“…Over recent years, topological superconductors (TSCs) have drawn much attention in condensed matters for the novel properties of Majorana zero boundary states [1][2][3][4] and the promising applications in quantum computation [5][6][7][8]. People find a lot of ways to realize and study the TSCs, including quantum dots [9][10][11][12][13][14], dopping topological insulators [15][16][17][18][19][20][21], promxity effect between topological insulators and superconductors [22][23][24][25][26][27], and arranging magnetic atomic on the surface of an swave with hlical structures [28][29][30][31][32][33][34][35][36] or SOC effect [37][38][39][40][41][42][43][44].…”