Resistive transitions of the superconductor were carried out under magnetic fields ranging from 0 to 8T. It was found that the irreversibility field Hirr(T) and the upper critical field HC2(T) obtained were very close to those determined in the magnetic measurements. By using the Arrhenius activation law, ρ = ρ0exp(-U/kT), the activation barrier U was determined by the low dissipation part of R(T) curves. It was found that U was much greater than kT; manifesting a very weak thermal activation and thermal fluctuation effect. This was a possible further indication that the flux dynamics near to Hirr(T) were induced by strong quantum fluctuation and the tunnelling of vortices.

Upper Critical Field and Irreversibility Line Determined by Transport Measurement of the New Superconductor MgB2. H.Jin, H.H.Wen, S.L.Li, Z.W.Zhao, Y.M.Ni, Z.A.Ren, G.C.Che, H.P.Yang, Z.Y.Liu, D.N.Zheng, Z.X.Zhao: Chinese Physics Letters, 2001, 18, 823-5