Muon Spin Rotation Studies of the Vortex Matter in the High-Tc Superconductor Bi2Sr2CaCu2O8+δ

T. Blasiusa, Ch. Niedermayera, J.L. Tallonb, D.M. Pookeb, A. Golnikc, D.R. Noakesd, C.E. Stronachd, E.J. Ansaldoe, R.W. Hennf, C.T. Linf and C. Bernhardf a Universität Konstanz, Fakultät für Physik, 78457 Konstanz, Germany b The New Zealand Institute for Industrial Research, P.O. Box 31310, Lower Hutt, New Zealand c Institute of Experimental Physics, Warsaw University, 00-681 Warsaw, Poland d Virginia State University, Petersburg, Virginia 23806, USA e University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 0W0 f Max-Planck-Institut für Festkörperforschung, 70569 Stuttgart, Germany

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We report muon spin rotation studies of the magnetic field distribution n(B) in the vortex state of the high-temperature superconductor Bi2Sr2CaCu2O8+δ. From our data on three sets of overdoped, nearly optimized and underdoped single crystals we obtain evidence for a two-stage melting process of the vortex matter under equilibrium conditions. In the irreversible regime well below the irreversibility line we observe a transition in the vortex state which we associate with an intra-planar melting transition. The resulting flux-line liquid phase persists over a sizeable temperature interval before the inter-planar decoupling of the individual vortex lines takes place in a second step at the irreversibility line, resulting in a pancake liquid phase.

DOI: 10.12693/APhysPolA.96.245 PACS numbers: 74.60.Ge, 74.25.Dw, 74.72.Hs, 76.75.+i