Fluctuation-induced diamagnetism above the superconducting transition inMgB2

Abstract

The behavior of the superconducting fluctuations in the normal state in ${\mathrm{MgB}}_{2}$ is studied through measurements of the fluctuation-induced diamagnetism (FD). These experiments show that the superconducting fluctuations in this compound are three dimensional in nature. Moreover, for reduced magnetic fields up to 0.5 the FD is not appreciably affected by nonlocal electrodynamic effects. This last FD behavior is in striking contrast with the one always observed, at equivalent reduced magnetic fields, in all other clean low-temperature metallic superconductors studied until now, but it is similar to the one found in cuprate superconductors. A sharp decrease of the fluctuation effects is observed around $\ensuremath{\varepsilon}=\mathrm{ln}{(T/T}_{C})\ensuremath{\approx}0.6,$ in agreement with recent results obtained in other low-${T}_{C}$ and high-${T}_{C}$ superconductors. This last result confirms the need of a total-energy cutoff condition to extend the applicability of the Gaussian-Ginzburg-Landau approach to the high reduced-temperature region.