The activation energy U(T,B) in high temperature superconductorAbdelaziz Labrag, Mustapha Bghour, Ahmed Abou El Hassan, Habiba El Hamidi, Ahmed Taoufik and Said LaasriEur. Phys. J. Appl. Phys., 92 2 (2020) 20601DOI: https://doi.org/10.1051/epjap/2020200223