Static and Dynamic Vortex Phases inYBa2Cu3O7−δ

Simultaneous magnetization, resistivity, and I-V measurements on ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ show the relationship of the thermodynamic and dynamic behavior near the vortex lattice melting line. We find a coexistence region of solid and liquid at melting, with a first order magnetization jump which is independent of the vortex velocity. Sudden jumps and time dependent hysteresis of the I-V curve in the vortex solid phase are interpreted as a relaxation-pinning effect.