Proximity Effect between Two Superconductors Spatially Resolved by Scanning Tunneling Spectroscopy

V Cherkez (1) , J. C. Cuevas (2) , C Brun (1) , T Cren (1) , G Ménard (1) , François Debontridder (1) , V. S. Stolyarov (3, 4, 1) , D Roditchev (5, 1)

1 INSP - Institut des Nanosciences de Paris
2 IFIMAC - Departamento de Física Teórica de la Materia Condensada and Condensed Matter Physics Center
3 MIPT - Moscow Institute of Physics and Technology [Moscow]
4 Russian Academy of Sciences - Chernogolovka
5 LPEM - Laboratoire de Physique et d'Etude des Matériaux (UMR 8213)

We present a combined experimental and theoretical study of the proximity effect in an atomic-scale controlled junction between two different superconductors. Elaborated on a Si(111) surface, the junction comprises a Pb nanocrystal with an energy gap Δ 1 ¼ 1.2 meV, connected to a crystalline atomic monolayer of lead with Δ 2 ¼ 0.23 meV. Using in situ scanning tunneling spectroscopy, we probe the local density of states of this hybrid system both in space and in energy, at temperatures below and above the critical temperature of the superconducting monolayer. Direct and inverse proximity effects are revealed with high resolution. Our observations are precisely explained with the help of a self-consistent solution of the Usadel equations. In particular, our results demonstrate that in the vicinity of the Pb islands, the Pb monolayer locally develops a finite proximity-induced superconducting order parameter, well above its own bulk critical temperature. This leads to a giant proximity effect where the superconducting correlations penetrate inside the monolayer a distance much larger than in a nonsuperconducting metal.

Domaines: Physique [physics]

V Cherkez, J. C. Cuevas, C Brun, T Cren, G Ménard, et al.. Proximity Effect between Two Superconductors Spatially Resolved by Scanning Tunneling Spectroscopy. Physical Review X, 2014, 4 (1), pp.011033. ⟨10.1103/PhysRevX.4.011033⟩. ⟨hal-01340115⟩