High-field quasiparticle tunneling in Bi₂ Sr₂ CaCu₂ O_{8 + δ}: Negative magnetoresistance in the superconducting state

Abstract

We report on the c-axis resistivity ρc(H) in Bi2 Sr2 CaCu2 O8 + δ that peaks in quasistatic magnetic fields up to 60 T. By suppressing the Josephson part of the two-channel (Cooper pair/quasiparticle) conductivity σc(H), we find that the negative slope of σq(H) above the peak is due to quasiparticle tunneling conductivity across the CuO2 layers below Hc2. At high fields (a) σq(H)grows linearly with H, and (b) ρc(T) tends to saturate (σc ≠ 0) as T → 0, consistent with the scattering at the nodes of the d-wave gap. A superlinear σq(H) marks the normal state above Tc. © 2000 American Physical Society.