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Thickness dependence of superconductivity for YBa2Cu3Oy ultra-thin films

Superconducting YBa2Cu3Oy ultra-thin films with thicknesses of 2-25 nm were deposited on (100) SrTiO3 substrates. The thickness dependence of superconductivity for YBa2Cu3Oy thin films was investigated. It was found that Tc showed only a small decrease for films with thickness greater than 15 nm, but dropped significantly when less than 10 nm. The variation of Tc with the film thickness fits an empirical relation of Tc0 = Tcbulk(1-dm/d). Based on this relation, a critical thickness dm = 1.56 nm was deduced, suggesting that superconductivity can be expected for one-unit-cell thick YBa2Cu3Oy films.