Evidence for two-dimensional nucleation of superconductivity in $\chem{MgB_2}$

A. S. Sidorenko; L. R. Tagirov; A. N. Rossolenko; V. V. Ryazanov; M. Klemm; R. Tidecks

doi:doi:10.1209/epl/i2002-00237-5

DOI: 10.1209/epl/i2002-00237-5

Europhys. Lett., 59 (2) , pp. 272-276 (2002)

Evidence for two-dimensional nucleation of superconductivity in $\chem{MgB_2}$

A. S. Sidorenko^{1, 2}, L. R. Tagirov^{1, 3}, A. N. Rossolenko⁴, V. V. Ryazanov⁴, M. Klemm¹ and R. Tidecks¹

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 in final form 23 April 2002)

Abstract
According to the crystal structure of $\chem{MgB_2}$ 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 $\un{nm}$ thick $\chem{MgB_2}$ films grown on $\chem{MgO}$ 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 $T_{\ab{c}}$ 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 $\chem{MgB_2}$ .

PACS
74.62.Bf - Effects of material synthesis, crystal structure, and chemical composition.
74.70.Ad - Metals; alloys and binary compounds (including A15, Laves phases, etc.).
74.76.-w - Superconducting films.

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