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Rise and fall of shape resonances in thin films of BCS superconductors

Published in Physical Review. B, Condensed Matter. 2016, vol. 94, no. 5, p. 054516
Abstract The confinement of a superconductor in a thin film changes its Fermi-level density of states and is expected to change its critical temperature Tc. Previous calculations have reported large discontinuities of Tc when the chemical potential coincides with a subband edge. By solving the BCS gap equation exactly, we show that such discontinuities are artifacts and that Tc is a continuous function of the film thickness. We also find that Tc is reduced in thin films compared with the bulk if the confinement potential is lower than a critical value, while for stronger confinement Tc increases with decreasing film thickness, reaches a maximum, and eventually drops to zero. Our numerical results are supported by several exact solutions. We finally interpret experimental data for ultrathin lead thin films in terms of a thickness-dependent effective mass.
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Research groups Groupe Giamarchi
Groupe Van der Marel
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VALENTINIS, Davide Filippo, VAN DER MAREL, Dirk, BERTHOD, Christophe. Rise and fall of shape resonances in thin films of BCS superconductors. In: Physical Review. B, Condensed Matter, 2016, vol. 94, n° 5, p. 054516. https://archive-ouverte.unige.ch/unige:87802

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Deposited on : 2016-09-27

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