First order phase transition at the irreversibility line ofBi2Sr2CaCu2O8

Abstract

Magnetization and susceptibility measurements show a first order phase transition in the magnetic flux structure at the irreversibility line of ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ single crystals, in the field range 0H360 Oe. The resistivity in the c direction drops 5 orders of magnitude in less than 0.1 K, and there is a discontiuous change in the magnetization at the same temperature. The change in magnetization together with the Clausius-Clapeyron equation gives a variation of entropy of 0.06${\mathit{k}}_{\mathit{B}}$ per vortex layer, at the transition. Above 360 Oe the irreversibility line has the known frequency dependence.