Superconducting Transition Temperature of Thin Films

Thickness dependence of the superconducting critical temperature in heavily doped Si:B epilayers

“…8 The importance of dimensionality has been further emphasized by the discovery of superconductivity at the interface of insulating oxides, 9 and the possible existence of high temperature superconductivity in single unit cell layers has been reported recently for FeSe deposited on SrTiO 3 . 10 However, other studies rather suggested a rapid suppression of T c with the sample thickness (d) in this later system (for d < 300 nm 11 ) and, except a few worth noting exceptions such as Al 12 or In, 13 superconductivity is generally destroyed in reduced dimensionality. [14][15][16] The critical thickness below which T c is suppressed can then vary from several hundreds of nm down to a few lattice constants, and understanding the interplay between quantum coherence, disorder, and electronic interactions in those confined geometries remains a major challenge.…”

“…If V 2 > V 1 ,d is negative and λ eff is expected to increase for decreasing d and this scenario could account for the increase of T c in very thin Al films 12 (assuming an enhanced electronphonon coupling on a surface layer of thickness d 2 ∼ a). On the contrary, if V 2 < V 1 , T c is expected to decrease with d, as observed in our Si:B films.…”

Superconductivity in mesoscopic high-Tc superconducting particles

“…Long time ago the studies of the superconducting-transion temperature T c of metallic films of Al, Sn, In, Zn prepared by vacuum deposition onto substrate held at cryogenic temperatures revealed the quantum size effect of the T c -oscillations with a film thickness [18][19][20][21][22][23][24] (see also review 25 ). In the simplest approaches 26-28 the quantum size effects follow from oscillations in the electronic density of states with thickness which in turn lead to oscillations with thickness of T c and other film quantities.…”

Surface superconductivity at high temperatures

“…There is some evidence that this situation has been observed, and that changes in the transition temperature on the order of a degree or so can occur [25][26][27][28][29]. Because these experiments have generally fallen within the region of validity of the Cooper limit and are described by the above result, it is reasonable to conjecture that d' > A for these systems; this is consistent with the likelihood that the mean free paths involved are short.…”

“…The interaction parameter V' is constant in a thin surface layer of thickness d', then falls abruptly to the bulk value V (we assume for simplicity that the density of states is constant). [25]. Since d' is typically much less than d, the effect of the surface layer is considerably diluted.…”