Evidence for two-dimensional nucleation of superconductivity in

¹ Institut für Physik, Universität Augsburg 86159 Augsburg, Germany
² Institute of Applied Physics - 2028 Kishinev, Moldova
³ Kazan State University - 420008 Kazan, Russia
⁴ Institute of Solid State Physics - 142432 Chernogolovka, Russia

Received: 3 December 2001
Accepted: 23 April 2002

Abstract

According to the crystal structure of and band structure calculations quasi–two-dimensional (2D) boron planes are responsible for the superconductivity. We report on critical fields and resistance measurements of 30 thick films grown on single crystalline substrate. A linear temperature dependence of the parallel and perpendicular upper critical fields indicates a 3D-like penetration of magnetic field into the sample. Resistivity measurements, in contrast, yield a temperature dependence of fluctuation conductivity above which agrees with the Aslamazov-Larkin theory of fluctuations in 2D superconductors. We consider this finding as an experimental evidence of two-dimensional nucleation of superconductivity in .