Anisotropic magnetoresistance of Bi2212 crystals

Abstract

In-plane resistance, Rab(B,T) in Bi2212 is studied under pulsed magnetic fields (perpendicular to the basal plane), B≤50 T both above and below Tc∼90 K. In contrast with the negative out-of-plane magnetoresistance (MR), the normal state in-plane MR is found to be positive. The absolute values of these MRs are found to be similar despite 4-5 orders of magnitude difference between the corresponding resistivities. These similarities, as well as the giant magnitude of the MRs, exceeding any orbital contribution by two orders of magnitude, could be broadly understood as the result of the breaking of preformed pairs by the magnetic field. The resistive upper critical fields Hc2(T), estimated from the in- and out-of-plane MRs taken below Tc, are approximately the same and reveal non-BCS temperature dependences compatible with the Bose-Einstein condensation field of preformed charged bosons. A significant reduction of the zero field R ab(T) is observed after extensive investigation of some crystals with numerous 50 T pulses. © 2004 Elsevier B.V. All rights reserved.