Direct Observation of Melting of the Vortex Solid inBi2Sr2CaCu2O8+δSingle Crystals

Abstract
A scanning Hall probe microscope has been used to directly observe the vortex lattice melting transition in Bi2Sr2CaCu2O8+δ single crystals. Below the melting line, the system settles into a fairly well-ordered vortex solid which undergoes pronounced rotations as the field is increased due to incommensurability effects. Vortex contrast is lost abruptly and discontinuously at the melting line consistent with a first order transition. Vortex profiles appear to be strongly broadened by two-dimensional fluctuations which grow much stronger as the melting line is approached from below, suggesting that melting and decoupling are almost simultaneous.