NEW FEATURES IN THE VORTEX PHASE-DIAGRAM OF YBA2CU3O7-DELTA

Magnetic and transport measurements have been performed in high qualit y YBa2Cu3O7-delta single crystals. We demonstrate for the first time t hat the magnetization peak line in the phase diagram of YBa2Cu3O7-delt a, H-p(T) exhibits an impressive similarity with the equivalent line f or Bi2Sr2CaCu2O8. Our results show not only a similar temperature depe ndence but also an almost identical response to oxygen doping and a co rrelation to the multicritical point. At high temperatures we observe a previously unreported splitting of the magnetization peak.