Seminar – Proximity Phenomena and Superconductivity in single atomic layers Pb/Si(111).

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Day / Time
Date(s) - 07/10/2014
13 h 00 min - 14 h 00 min


Ecole de Physique, Auditoire Stueckelberg, 24 quai Ernest-Ansermet


Proximity Phenomena and Superconductivity in single atomic layers Pb/Si(111).

Tristan Cren, C. Brun, L. Serrier-Garcia, S. Pons, V. Cherkez, F. Debontridder
Institut des Nanosciences de Paris (INSP), CNRS &Université Paris 6 (UPMC), France

L. Ioffe
Laboratoire de Physique Theorique et Hautes Energies, CNRS &Université Paris 6 (UPMC), France

B. Altshuiler
Physics Department, Columbia University, New York, New York 10027, USA

D. Roditchev
Laboratoire de Physique et d’Etude des Matériaux (LPEM), CNRS &ESPCI, Paris, France

In 1964 V. L. Ginzburg predicted that new superconducting phases could appear in ultrathin films deposited on insulators. In order to get some insight on this question we studied single atomic layers of Pb grown on atomically clean Si(111), by scanning tunneling spectroscopy at very low temperature (0.3-2K). The monolayers can be on-demand made amorphous or crystalline with various reconstructions.
We found that the as-grown amorphous Pb monolayer is non-superconducting down to 0.3K; rather, it behaves like a ‘bad’ correlated metal. When put in contact with a superconductor, it acquires superconducting correlations which evolve on a global Altshuler-Aronov spectral background [1].

Contrary to the amorphous Pb/Si(111), several reconstructed Pb-phases become superconducting below 2K. We analyzed this superconductivity at nanometer scale [2]. While we observed a quite conventional general superconducting behavior, several exotic phenomena, unrevealed in conventional bulk superconductors, were discovered. We found that i) – the superconducting wave function is strongly confined at the Pb/Si interface, and does not propagate in the bulk substrate beyond 2-3 atomic layers; ii) – the vortex phase is peculiar and is composed of two kinds of vortices, and iii) – the tunneling characteristics evolve at very short length scales, much shorter than superconducting coherence length ξ [3]. In our talk we discuss possible origins of the observed phenomena.

[1] L. Serrier-Garcia, et al. Phys. Rev. Lett. 110, 157003 (2013)
[2] V.Cherkez, et al. Phys. Rev. X 4, 011033 (2014)
C. Brun, et al., Nature Phys. 2014, DOI 10.1038/nphys2937 (in print)



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