Temperature and field dependence of thermally activated flux flow   resistance in Bi2Sr2CaCu2O8+{\delta} superconductor
  We study the temperature dependence of the resistivity as a function of magnetic field in superconducting transition (Tconset - TcR=0) region for different Bi2Sr2CaCu2O8+{\delta} superconducting samples being synthesized using sol-gel method. The superconducting transition temperature (TcR=0) of the studied samples is increased from 32 K to 82K by simply increasing the final sintering temperature with an improved grains morphology. On the other hand, broadening of transition is increased substantially with decrease in sintering temperature; this is because Tconset is not affected much with grains morphology. Further broadening of the superconducting transition is seen under magnetic field, which is being explained on the basis of thermally activated flux flow (TAFF) below superconducting transition temperature (Tc). TAFF activation energy (U0) is calculated using the resistive broadening of samples in the presence of magnetic field. Temperature dependence of TAFF activation energy revealed linear temperature dependence for all the samples. Further, magnetic field dependence is found to obey power law for all the samples and the negative exponent is increased with increase in sintering temperature or the improved grains morphology for different Bi-2212 samples. We believe that the sintering temperature and the ensuing role of grain morphology is yet a key issue to be addressed in case of cuprate superconductors. 
Devina Sharma (NPL New Delhi-12 and Panjab Univ. Chandigarh), Ranjan   Kumar (Panjab Univ. Chandigarh, India) and V. P. S. A...
cond-mat.supr-con