Thermal fluctuation and upper critical field of MgB2 superconductor

We have investigated the magnetic and transport properties of MgB2 superconductor over wide temperature and magnetic ranges. The upper critical fields Hc2 are determined by the scaling analysis of the thermal fluctuation magnetoconductivity. Around the transition region, the thermal fluctuation magnetoconductivity can be scaled by a universal function for all applied magnetic fields. The formula Hc2(T)=Hc2(0)[1−(T/Tc)3/2]3/2 of a narrow-band pairing mechanism gives an excellent fit to the data. Based on the value of upper critical field Hc2(0)=155 kOe, the superconducting coherence length is determined to be 4.6 nm. The Ginzburg–Landau parameter κ is 50 in the MgB2 superconducting system.