Two-band theory of specific heat and thermal conductivity in the mixed state of MgB_2

Abstract

We solve the coupled gap equations for the $\sigma$- and $\pi$-bands of MgB${}_2$ in the vortex state and calculate the resulting field dependencies of the specific heat coefficient $\gamma$ and the thermal conductivity $\kappa$. The crucial parameters of the theory are the interband pairing interaction ${\lambda }_{\pi \sigma }$ and the ratio $s={\xi }_{\sigma }/{\xi }_{\pi }$ of the coherence lengths. For reasonably small ${\lambda }_{\pi \sigma }$ and s, the small gap ${\Delta }_{\pi }$ decreases with increasing magnetic field $H$ much faster than the large gap ${\Delta }_{\sigma }$. This gives rise to the observed rapid increase of ${\gamma }_{\pi }$ and ${\kappa }_{\pi }$ for small fields while ${\gamma }_{\sigma }$ and ${\kappa }_{\sigma }$ exhibit conventional field dependencies. Inclusion of intraband impurity scattering yields fairly good agreement with experiments for applied fields along the c axis.

4 pages, 3 figures, Accepted by Phys. Rev. B

References in corpus (5)

• Vortex Imaging in the pi-Band of Magnesium Diboride
• Electronic Structure, Electron-Phonon Coupling, and Multiband Effects in MgB2
• Specific heat of single crystal MgB_2: a two-band superconductor with two different anisotropies
• Fermi surface topology and the upper critical field in two-band superconductors - application to MgB2
• Specific heat and thermal conductivity in the vortex state of the two-gap superconductor MgB_2

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• Influence of carbon substitution on the heat transport in single crystalline MgB2
• Thermal conductivity of Al-doped MgB2: Impurity scattering and the validity of the Wiedemann-Franz law