Fluctuation Effects in Mixed State of Type II Superconductor. Comparison of Experimental Results with Theoretical Predictions

Abstract

Results of the investigation of fluctuation phenomena in bulk type-II superconductors obtained in 1980 - 1984 years are compared with the analogous results obtained at the investigation of high-Tc superconductors (HTSC). It is shown the latter repeat in the main the results obtained before the HTSC discovery. It was discovered in 1981 year that a sharp change of resistive properties is observed below the second critical field, at H_{c4} < H_{c2}, in high quality samples of type-II superconductors. The same was repeated at investigation of high quality HTSC samples and was interpreted as vortex lattice melting. The difference of the (H_{c2} - H_{c4}) values for low- and high-Tc superconductors corresponds with the scaling law obtained in the lowest Landau level approximation. The linear approximation region above H_{c2}, the critical region and the Abrikosov state are considered. It is emphasized that the rigorous Ami-Maki theory should be used for description of paraconductivity in HTSC and &#34;dirty&#34; conventional superconductors. The approximation dependencies obtained from popular Aslamasov-Larkin, Hikami-Larkin and Lawrence-Doniac works do not have a validity region in these superconductors with wide critical region.