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What happens to the pairing correlations in a cuprate superconductor when superconducting order is suppressed with a magnetic field? We have studied this problem in LBCO x=1/8, where 2D superconductivity appears below 40 K, but 3D order only occurs below 5 K, presumably due to pair-density-wave order intertwined with the spin- and charge-stripe orders. At T = 0.35 K, a c-axis magnetic field initially induces finite dissipation near 10 T, followed by re-entrant 2D superconductivity between 18 and 22 T [1]. The resistance per CuO₂ plane rises to h/(4e²) near 31 T, but then saturates at 2h/(4e²) at higher fields. The saturation of the resistance indicates metallic behavior, but the fact that the Hall coefficient is ~ 0 indicates a lack of quasiparticles. We conclude that conduction is by incoherent hopping of pairs between charge stripes, indicating that stripes are good for pairing, but not phase coherence.
[1] Y. Li et al., arXiv:1810.10646.