title: Excess conductivity and Berezinskii-Kosterlitz-Thouless transition in superconducting FeSe thin films.
abstract: Temperature-dependent electronic transport in the vicinity of the superconducting transition is reported for quasi-two-dimensional textured FeSe thin films. The conspicuous rounding of the resistive transitions and large transition widths are indications of excess conductivity due to thermal Cooper-pair fluctuations, which can be well-described by the two-dimensional Aslamazov-Larkin theory. The Halperin-Nelson form of the sheet resistance between the phase-ordering temperature TBKT and the mean-field temperature TMF, and the power-law behaviour of the voltage-current characteristics, with a distinctive jump of the exponent at TBKT, are indicative of a Berezinskii-Kosterlitz-Thouless transition. The complementary results suggest a two-dimensional character of superconductivity in the FeSe films and allow a quantitative estimate of the Ginzburg number Gi.
authors.affiliation: Institut für Festkörperphysik, Karlsruher Institut für Technologie, D-76021 Karlsruhe, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Schneider
authors.forename: A G
authors.initials: AG
authors.lastname: Zaitsev
authors.forename: D
authors.initials: D
authors.lastname: Fuchs
authors.forename: H
authors.initials: H
authors.lastname: von Löhneysen