Weak inter-band coupling in Mg${}^{10}$B${}_2$: a specific heat analysis

Abstract

The superconducting state of Mg${}^{10}$B${}_2$ is investigated by specific heat measurements in detail. The specific heat in the normal state is analyzed using a recently developed computer code. This allows for an extraction of the electronic specific heat in the superconducting state with high accuracy and a fair determination of the main lattice features. One of the two investigated samples shows a hump in the specific heat at low temperatures within the superconducting state, accompanied by an unusual low value of the small gap, ${\Delta }_{\pi }(0)=1.32meV$, pointing to a very weak inter-band coupling. This sample allows for a detailed analysis of the contribution from the $\pi$-band to the electronic specific heat in the superconducting state. Therefore the usual analysis method is modified, to include the individual conservation of entropy of both bands. From analyzing the deviation function $D(t)$ of MgB${}_2$, the theoretically predicted weak inter-band coupling scenario is confirmed.

major revisions

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• A review of two-band superconductivity: materials and effects on the thermodynamic and reversible mixed-state properties
• Stable fractional flux vortices in mesoscopic superconductors
• Thermodynamically stable noncomposite vortices in mesoscopic two-gap superconductors
• Point-contact spectroscopy of the nickel borocarbide superconductors RNi2B2C (R=Y, Dy, Ho, Er, Tm, Lu)
• Effect of interband interactions of phonon and charge fluctuation on superconducting parameters of MgB2
• Two-gap superconductivity: interband interaction in the role of external field