MAGNETIC PHASE-DIAGRAMS FOR HIGH TRANSITION-TEMPERATURE SUPERCONDUCTORS

Recent measurements of the dissipation in cuprate superconductors in a magnetic field have been interpreted as providing evidence for the presence of new phases, such as flux liquids or flux glasses, in type-II superconductors. We suggest that a more conventional interpretation in terms of the electrodynamics of vortices can adequately account for all the observations. Based on this model, we propose a magnetic phase diagram. We show that the phase diagram is dramatically influenced by the effective length of the flux lines. When the flux lines are long (i.e., three dimensional), the conventional picture of a robust Abrikosov lattice weakly pinned to the defects still applies at moderate magnetic fields far from Tc and flux lattice melting may only appear at low magnetic fields over an extended temperature range. If the flux lines are two-dimensional, the region of the phase diagram occupied by melting enlarges considerably. © 1990.