Abstract:

The vortex-matter phase diagram of Tl2Ba2CaCu2O8+x single crystal superconductor has been studied, using bulk and local magnetization measurements. We observed a second magnetization peak in the temperature interval 20 K < T < 40 K. At 40 K the second peak splits into two peaks, termed the upper and lower second magnetization peaks (USP and LSP), respectively. In the magnetic field interval [H-LCP,H-UCP] we observed the clear signature of a first-order melting transition of the vortex lattice. This particular behavior is similar to a situation with two critical endpoints of the first-order melting line and one coexistence point, where the topological transition line ends on the first-order melting line.