Thermal fluctuation and upper critical field of MgB2 superconductor

Abstract We have investigated the magnetic and transport properties of MgB 2 superconductor over wide temperature and magnetic ranges. The upper critical fields H c2 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 H c2 ( T )= H c2 (0)[1−( T / T c ) 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 H c 2 (0)=155 kOe , the superconducting coherence length is determined to be 4.6 nm. The Ginzburg–Landau parameter κ is 50 in the MgB 2 superconducting system.