Fluctuation study of the specific heat ofMg11B2

Abstract

The specific heat of polycrystalline ${\mathrm{Mg}}^{11}{\mathrm{B}}_{2}$ has been measured with high-resolution ac calorimetry from 5 to 45 K at constant magnetic fields. The excess specific heat above ${T}_{c}$ is discussed in terms of Gaussian fluctuations and suggests that ${\mathrm{Mg}}^{11}{\mathrm{B}}_{2}$ is a bulk superconductor with Ginzburg-Landau coherence length ${\ensuremath{\xi}}_{0}=26\mathrm{\AA{}}.$ The transition-width broadening in field is treated in terms of lowest-Landau-level (LLL) fluctuations. That analysis requires that ${\ensuremath{\xi}}_{0}=20\mathrm{\AA{}}.$ The underestimate of the coherence length in field, along with deviations from three-dimensional LLL predictions, suggests that there is an influence from the anisotropy of ${B}_{c2}$ between the c axis and $a\ensuremath{-}b$ plane.