Unified order-disorder vortex phase transition in high-Tcsuperconductors

The diversity of vortex melting and solid-solid transition lines measured in different high-T c superconductors is explained, postulating a unified order-disorder phase transition driven by both thermally- and disorder-induced fluctuations. The temperature dependence of the transition line and the nature of the disordered phase (solid, liquid, or pinned liquid) are determined by the relative contributions of these fluctuations and by the pinning mechanism. By varying the pinning mechanism and the pinning strength one obtains a spectrum of monotonic and nonmonotonic transition lines similar to those measured in Bi 2 Sr 2 CaCu 2 O 8 , YBa 2 Cu 3 O 7 - Φ , Nd 1 . 8 5 Ce 0 . 1 5 CuO 4 - Φ , Bi 1 . 6 Pb 0 . 4 Sr 2 CaCu 2 O 8 + Φ , and (La 0 . 9 3 7 Sr 0 . 0 6 3 ) 2 CuO 4 .