Fluctuation Effects in Mixed State of Type II Superconductor
Investigation of the fluctuation phenomena changes habitual notion about the mixed state of type II superconductors. Before the fluctuation investigation one thought that the second-order phase transition from the normal state into the Abrikosov state takes place in the second critical field, Hc2 [1]. Now it is clear that a phase transition in Hc2 is absent and the transition in the Abrikosov state, called now often as “vortex lattice melting”, occurs below Hc2 [2] Now it is widely recognized that the normal state with superconducting fluctuation, called as “vortex liquid”, exists not only above but also below Hc2 [2] This becomes widely known in the last time, after the investigation of the fluctuation phenomena in high-Tc superconductors (HTSC) Therefore most of scientists connect these changes of the habitual notion about the mixed state with the HTSC investigation first of all Moreover some authors suppose that these changes of the notion relate to HTSC only because they think that the fluctuation effects in conventional superconductors are very small [3]. But it is not right. Moreover just the investigation of the fluctuation phenomena of conventional superconductors have shown first that the transition into the Abrikosov state occurs below Hc2 It was made before the HTSC discovery. But these result are not enough known. Therefore I will write about these results first of all in this report I will show that the results obtained on high quality samples of YBa2Cu3O7-x repeat in the main our results obtained by the investigation of bulk conventional superconductors. In the end I will discuss the main unsolved problem - the nature of the transition into the Abrikosov state