Fluctuation Study of the Specific Heat of MgB2

TL;DR

This study measures the specific heat of MgB2 to analyze superconducting fluctuations, revealing insights into its coherence length, fluctuation effects, and anisotropic properties near the transition temperature.

Contribution

It provides high-resolution calorimetry data and analyzes fluctuation effects, offering new estimates of the coherence length and evidence of anisotropy in MgB2.

Findings

Coherence length estimated at 26 Å from Gaussian fluctuations.

Transition broadening in magnetic field explained by LLL fluctuations.

Anisotropy influences the superconducting properties and fluctuation behavior.

Abstract

The specific heat of polycrystalline Mg$^{11}$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 Mg$^{11}$B$_{2}$ is a bulk superconductor with Ginzburg-Landau coherence length $\xi_{0}=26$ \AA . The transition-width broadening in field is treated in terms of lowest-Landau-level (LLL) fluctuations. That analysis requires that $\xi_{0}=20$ \AA . The underestimate of the coherence length in field, along with deviations from 3D LLL predictions, suggest that there is an influence from the anisotropy of B$_{c2}$ between the c-axis and the a-b plane.