Thermally-activated vortex dynamics in bismuth calcium strontium copper oxide (Bi2CaSr2Cu2O8+δ) studied by complex susceptibility measurements

Complex AC magnetic susceptibility has been measured on Bi2CaSr2Cu2O8+d single crystals with hnc, Hdc|c-axis. It will be shown that field, frequency and temperature dependence of both ¿' and ¿¿ in a constant but sufficiently large DC magnetic field can quantitatively be described by thermally-activated flux flow (TAFF) provided that a narrow distribution of activation energies is implemented. From the frequency dependence of the AC¿ transition, a power law for the DC field dependence of the activation energy has been found, with an exponent -1/4