Study of superconducting properties of MgB2

TL;DR

This study investigates the superconducting properties of MgB2, including crystal structure, specific heat, and magnetic behavior, revealing deviations from conventional BCS theory and anisotropic superconductivity.

Contribution

The paper provides detailed synthesis, structural analysis, and thermodynamic measurements of MgB2, highlighting its unconventional superconducting characteristics and anisotropy.

Findings

Single crystals of MgB2 were successfully synthesized with high quality.

The specific heat measurements indicate deviations from BCS weak coupling theory.

Superconducting transition temperature is around 38 K with notable anisotropy.

Abstract

We synthesized single crystalline and policrystalline MgB_2 under ambient pressures. The single crystals of MgB_2 were of good quality, where the crystal structure refinements were successfully converged with R = 0.020. The specific heat of policrystalline MgB_2 samples has been measured in a temperature range between 2 and 60 K in magnetic field up to 6 T. The measurement gave the coefficient of the linear term in the electronic specific heat, gamma = 3.51 mJ/K^2 mol, and the jump of the specific heat, 2.8 mJ/K^2 mol at 38.5 K. It is shown from the analysis of the specific heat that the electronic specific heat in the superconducting state differs largely from the conventional BCS weak coupling theory. From the results of measurements of the magnetic properties on single crystal samples, we found a sharp superconducting transition at 38 K with transition width Delta Tc = 0.8 K and the superconducting anisotropy ratio gamma increasing from about 1 near Tc to 4.0 at 25 K.