Dependence of the Energy Gap in Tin Films on Magnetic Field and Film Thickness by Electron Tunnelling

概要

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By the electron tunnelling technique, the energy gap $2\varDelta$ in superconducting tin films with various thickness $d$ ranging from 3670 Å to 420 Å was measured as a function of temperature $T$ and magnetic field $H$ parallel to the plane of the tin film. Temperature dependence of $2\varDelta$ is almost the same for all tin films, and the mean value of $2\varDelta(0)/kT_{c}$ is 3.57, where $2\varDelta(0)$ means the energy gap at 0°K. As for the behaviours in magnetic field, i.e. $H$ dependence of $2\varDelta$ and thickness dependence of the critical field determined from $2\varDelta$–$H$ curves, there are marked differences among the films, $d{>}1900$ Å, 1900 Å${>}$$d$${>}$ca. 700Å and $d$${<}$ca. 700 Å. Those of the films thicker than 1900 Å agree with the local theories by Ginzburg-Landau-Gor'kov-Douglass and Ginzburg-Landau respectively, while those of the films with medium thickness, 1900 Å${>}$$d$${>}$ca. 700 Å, are consistent with the non-local theories by Casella-Miller or Nambu-Tuan qualitatively. However for the thickness region, $d$${<}$ca. 700 Å, there is no theory to explain the experimental results in magnetic field, but if type two superconductivity is assumed for these very thin films, a reasonable explanation can be given.
Physical Society of Japanの論文
1968-01-05