First-order disorder-driven transition and inverse melting of the vortex   lattice
  Vortex matter phase transitions in the high-temperature superconductor Bi2Sr2CaCu2O8 were studied using local magnetization measurements combined with a vortex 'shaking' technique. The measurements revealed thermodynamic evidence of a first-order transition along the second magnetization peak line, at temperatures below the apparent critical point Tcp. We found that the first-order transition line does not terminate at Tcp, but continues down to at least 30 K. This observation suggests that the ordered vortex lattice phase is destroyed through a unified first-order transition that changes its character from thermally induced melting at high temperatures to a disorder-induced transition at low temperatures. At intermediate temperatures the transition line shows an upturn, which implies that the vortex matter displays 'inverse' melting behavior. 
Nurit Avraham, Boris Khaykovich, Yuri Myasoedov, Michael Rappaport,   Hadas Shtrikman, Dima E. Feldman, Eli Zeldov, Tsuyoshi...