High-field quasiparticle tunneling in Bi2Sr2CaCu2O8+δ:: Negative magnetoresistance in the superconducting state

We report on the c-axis resistivity rho(c)(H) in Bi2Sr2CaCu2O8+delta that peaks in quasistatic magnetic fields up to 60 T. By suppressing the Josephson part of the two-channel (Cooper pair/quasiparticle) conductivity sigma(c)(H), we find that the negative slope of rho(c)(H) above the peak is due to quasiparticle tunneling conductivity a,(H) across the CuO2 layers below H-c2. At high fields (a) sigma(q),(H) grows linearly with H, and (b) rho(c)(T) tends to saturate (sigma(c) not equal 0) as T --> 0, consistent with the scattering at the nodes of the d-wave gap. A superlinear sigma(q)(H) marks the normal state above T-c.