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Issue Europhys. Lett.
Volume 60, Number 1, October 2002
Page(s) 134 - 140
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
DOI 10.1209/epl/i2002-00330-9

DOI: 10.1209/epl/i2002-00330-9


Europhys. Lett., 60 (1) , pp. 134-140 (2002)

Anisotropic s-wave superconductivity: Comparison with experiments on $\chem{MgB_2}$ single crystals

A. I. Posazhennikova1, 2, T. Dahm3, 4 and K. Maki4, 5

1  Laboratorium voor Vaste-Stoffusica en Magnetisme, Katholieke Universiteit Leuven B-3001 Leuven, Belgium
2  Max-Planck-Institute for the Chemical Physics of Solids Nöthnitzer Str. 40, D-01187 Dresden, Germany
3  Universität Tübingen, Institut für Theoretische Physik Auf der Morgenstelle 14, 72076 Tübingen, Germany
4  Max-Planck-Institute for Physics of Complex Systems Nöthnitzer Str. 38, D-01187 Dresden, Germany
5  Department of Physics and Astronomy, University of Southern California Los Angeles, CA 90089-0484, USA

(Received 4 April 2002; accepted in final form 9 July 2002)

Abstract
The recently discovered superconductivity in MgB 2 has captured world attention due to its simple crystal structure and relatively high superconducting transition temperature $T_{\rm c}=39\un{K}$. It appears to be generally accepted that it is phonon-mediated s-wave BCS-like superconductivity. Surprisingly, the strongly temperature-dependent anisotropy of the upper critical field, observed experimentally in magnesium diboride single crystals, is still lacking a consistent theoretical explanation. We propose a simple single-gap anisotropic s-wave order parameter in order to compare its implications with the predictions of a multi-gap isotropic s-wave model. The quasiparticle density of states, thermodynamic properties, NMR spin-lattice relaxation rate, optical conductivity, and $H_{\rm c2}$ anisotropy have been analyzed within this anisotropic s-wave model. We show that the present model can capture many aspects of the unusual superconducting properties of the MgB 2 compound, though more experimental data appear to be necessary from single-crystal MgB 2.

PACS
74.20.Rp - Pairing symmetries (other than s-wave).
74.25.Bt - Thermodynamic properties.
74.70.Ad - Metals; alloys and binary compounds (including A15, Laves phases, etc.).


© EDP Sciences 2002


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