Anisotropic s-wave superconductivity: comparison with experiments on MgB2 single crystals

Abstract

The recently discovered superconductivity in MgB2 has captured world attention due to its simple crystal structure and relatively high superconducting transition temperature Tc=39K. 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 prediction of a multi-gap isotropic s-wave model. The quasiparticle density of states, thermodynamic properties, NMR spin-lattice relaxation rate, optical conductivity, and Hc2 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 MgB2 compound, though more experimental data appear to be necessary from single crystal MgB2.

7 pages, 6 figures, some minor changes, to appear in Europhys. Lett

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• Definitive experimental evidence for two-band superconductivity in MgB2
• A review of two-band superconductivity: materials and effects on the thermodynamic and reversible mixed-state properties
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• Optical spectroscopy of superconducting Ba{0.55}K{0.45}Fe2As2: evidence for strong coupling to low energy bosons
• Anisotropy of superconducting single crystal SmFeAsO_(0.8)F_(0.2) studied by torque magnetometry
• Spectrum of low energy excitations in the vortex state: comparison of Doppler shift method to quasiclassical approach
• Anomalous microwave conductivity coherence peak in c-axis MgB2 thin film
• Unusual effects of anisotropy on the specific heat of ceramic and single crystal MgB2
• Microwave Response of V3Si Single Crystals: Evidence for Two-Gap Superconductivity
• Strongly Anisotropic s-Wave Gaps in Exotic Superconductors
• Angular-dependent upper critical field of overdoped Ba(Fe${}_{1-x}$Ni${}_x$)${}_2$As${}_2$
• Fermi surface topology and vortex state in MgB2
• Basal-Plane Magnetic Anisotropies of High-kappa d-Wave Superconductors in a Mixed State: A Quasiclassical Approach
• Superconductivity of Magnesium Diboride: Theoretical Aspects
• Far-infrared and submillimeter-wave conductivity in electron-doped cuprate La_{2-x}Ce_xCuO_4