title: Localization and interaction effects in ultrathin epitaxial NbN superconducting films.
abstract: For epitaxial NbN films with thickness d, 2.0 nm ≤ d ≤ 20.5 nm, we observed a sharp superconducting transition, for which the transition temperature T(c) monotonically decreased with increasing 1/d. Regarding the suppression of T(c), the sheet resistance R(sq) dependence of T(c) closely fitted the Finkel'stein formula from localization theory, with a reasonable value of the electron mean free path comparable to atomic distance, which was used as a fitting parameter. On the other hand, the critical sheet resistance R(c), at which the superconducting-insulator transition was expected, was approximately one-third of the universal value R(q) = h/4e(2) suggested by the dirty boson model for self-duality. It is concluded that T(c) depression in the present NbN system is determined by localization theory but not the dirty boson model.
authors.affiliation: Department of Physics, Kyushu University, Fukuoka 810-8560, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Ezaki
authors.forename: K
authors.initials: K
authors.lastname: Makise
authors.forename: B
authors.initials: B
authors.lastname: Shinozaki
authors.forename: T
authors.initials: T
authors.lastname: Odo
authors.forename: T
authors.initials: T
authors.lastname: Asano
authors.forename: H
authors.initials: H
authors.lastname: Terai
authors.forename: T
authors.initials: T
authors.lastname: Yamashita
authors.forename: S
authors.initials: S
authors.lastname: Miki
authors.forename: Z
authors.initials: Z
authors.lastname: Wang