Coherence lengths and anisotropy in MgB2 superconductor

TL;DR

This study investigates the coherence lengths and anisotropy ratios in MgB2 superconductors through microwave measurements, revealing distinct anisotropy values in the mixed state and at the transition, with implications for understanding superconducting properties.

Contribution

It provides new measurements of coherence lengths and anisotropy ratios in MgB2, highlighting differences between the mixed state and transition, and demonstrating temperature independence of these parameters.

Findings

Mean field coherence length and anisotropy ratio determined

Ginzburg-Landau coherence length and anisotropy ratio measured at transition

Anisotropy ratios are temperature independent

Abstract

Field and temperature microwave measurements have been carried out on MgB2 thin film grown on Al2O3 substrate. The analysis reveals the mean field coherence length xi_{MF} in the mixed state and a temperature independent anisotropy ratio gamma_{MF} = xi_{MF}^{ab} / xi_{MF}^c approximately 2. At the superconducting transition, the scaling of the fluctuation conductivity yields the Ginzburg-Landau coherence length with a different anisotropy ratio gamma_{GL} = 2.8, also temperature independent.