QDev Seminar: Gerbold Ménard

Institut des NanoSciences de Paris

Local magnetic interaction in 2D Superconductors: From Shiba bound states to Majorana quasiparticles

G. Ménard1, S. Guissart2, C. Brun1, F. Debontridder1, R. Leriche1, S. Pons3, D. Roditchev3, P. Simon2, T. Cren1

1Institut des Nanosciences de Paris, Sorbonne Universités, UPMC Univ. Paris 6 and CNRS-UMR 7588, F-75005 Paris, France 2Laboratoire de Physique des solides, Université Paris-Sud, 91405 Orsay, France
3Laboratoire de Physique et d’étude des matériaux, LPEM-UMR8213/CNRS-ESPCI Paris Tech-UPMC, 10 Rue Vauquelin, 75005 Paris, France

In recent years Majorana excitations in superconductors became a widely studied subject in condensed matter physics both theoretically and experimentally. The excitement surrounding this research is due to the potential applications to quantum information of the non-trivial statistics associated to these excitations. The two ingredients one needs in order to observe these excitations in a superconductor are spin-orbit interaction and magnetism.

By using low temperature (300 mK) scanning tunneling microscopy and spectroscopy we studied individual localized magnetic moments as well as large magnetic clusters. I will present here the results obtained in the 2D system that the Pb/Si monolayer is. Using a 2D system provides a strong Rashba spin-orbit interaction [1] that will give rise to a mixture of singlet and triplet superconductivity [2].

In my presentation I will first describe the properties of individual magnetic impurities giving rise to Yu-Shiba-Rusinov (YSR) bound states. The spatial extent of these states is directly linked to the dimensionality of the system [3] and the spatial pattern of the local density of states surrounding the magnetic atoms is determined by the structure of the Fermi surface. In the case of a disordered system, the spatial structure of the YSR bound states follows a speckle pattern caused by the incoherent diffusion of electrons by the atomic lattice. By growing magnetic nanostructures of a size about 10 nm we evolve from isolated in-gap states to a continuum of states. At the Fermi level the spectroscopic features of these structures do not show any sensitivity to the locally disordered atomic structure and present a linear dispersion of the in-gap states indicative of a topological protection of said states.

[1] A. V. Matetskiy et al. Two-dimensional superconductor with a giant Rashba effect: One-atom-layer Tl-Pb compound on Si(111). Phys. Rev. Lett., 115, 147003 (2015)
[2] L. P. Gor’kov and E. I. Rashba, Superconducting 2D system with lifted spin-degeneracy: mixed singlet- triplet state. Phys. Rev. Lett., 87, 037004 (2001)

[3] G. Ménard et al. Coherent long-range magnetic bound states in a superconductor. Nat. Phys. 11, 1013 (2015)