Observation of the First-Order Vortex Lattice Melting in NdBa_2Cu_3O_(7-y) Single Crystals

摘要

We have observed the first-order melting transition for the first time in twinned NdBa_2Cu_3O_(7-y) single crystal that was previously thought to be a non-stoichiometric system. The transition displays a 'kink' in resistance and a jump in magnetization. The V-I characteristics in field exhibit a characteristic S shape behavior at the melting transition. We observed the hysteresis in magnetoresistance near the kink region. We obtain mass anisotropy, #gamma#=5.9 and c_L=0.16 consistent with the melting criterion. The magnetic phase diagram obeys the melting scaling.. This is the first observation of a first-order melting transition in a system other than YBCO containing magnetic rareearth ions. Our results clearly demonstrate that NdBCO single crystal, grown by flux method under reduced partial oxygen pressure, behaves as a "clean" superconductor.