Yu–Shiba–Rusinov screening of spins in double quantum dots

• Published in: Nature communications Vol. 9; no. 1; pp. 2376 - 6
• Main Authors: Grove-Rasmussen, K., Steffensen, G., Jellinggaard, A., Madsen, M. H., Žitko, R., Paaske, J., Nygård, J.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 18.06.2018; Nature Publishing Group; Nature Portfolio
• Subjects: 639/766/119/1003; 639/766/119/995; 639/925/927/1007; 639/925/927/1064; Arsenides; Conductance; Coupling; Energy gap; Gating; Honeycomb construction; Humanities and Social Sciences; Impurities; Indium; Indium arsenides; Mathematical models; multidisciplinary; Nanotechnology; Nanowires; Quantum dots; Resistance; Science; Science (multidisciplinary); Screening; Switches; Topology
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-018-04683-x

A magnetic impurity coupled to a superconductor gives rise to a Yu–Shiba–Rusinov (YSR) state inside the superconducting energy gap. With increasing exchange coupling the excitation energy of this state eventually crosses zero and the system switches to a YSR ground state with bound quasiparticles screening the impurity spin by ħ /2. Here we explore indium arsenide (InAs) nanowire double quantum dots tunnel coupled to a superconductor and demonstrate YSR screening of spin-1/2 and spin-1 states. Gating the double dot through nine different charge states, we show that the honeycomb pattern of zero-bias conductance peaks, archetypal of double dots coupled to normal leads, is replaced by lines of zero-energy YSR states. These enclose regions of YSR-screened dot spins displaying distinctive spectral features, and their characteristic shape and topology change markedly with tunnel coupling strengths. We find excellent agreement with a simple zero-bandwidth approximation, and with numerical renormalization group calculations for the two-orbital Anderson model. Coupling superconductors to mesoscopic systems leads to unusual effects that could be exploited in new devices including topological quantum computers. Here the authors present a double quantum dot with a Yu–Shiba–Rusinov ground state arising from the interplay of Coulomb interactions and superconductivity.