Investigations of the vortex matter in Bi[sub 2]Sr[sub 2]Ca[sub 1]Cu[sub 2]O[sub 8+δ] single crystals

We report transverse-field muon spin rotation studies of the magnetic field distribution n(B) in the vortex state of the high temperature superconductor Bi2Sr2Ca1Cu2O8+δ (Bi-2212) and present data on three sets of overdoped, nearly optimized and underdoped single crystals which to our best knowledge provide the first evidence that a two-stage melting transition of the vortex matter occurs under equilibrium conditions. In addition, we compare the TF-μSR results with those from DC-magnetization measurements and magneto-optic experiments on the same crystals.