Null Orbital Frustration at the Pseudogap Boundary in a Layered Cuprate Superconductor

We assess the relative importance of orbital frustration at the pseudogap closing field H_pg. Using interlayer tunneling transport in pulsed magnetic fields nearly up to 60 T, we track the field-temperature (H-T) phase diagram for fields parallel (∥ab) and normal (∥c) to the layered structure of Bi₂Sr₂CaCu₂O_8+y. In contrast to large orientational anisotropy of the superconducting state related to the orbital motion of Cooper pairs, we find anisotropy of H_pg temperature independent and small, due solely to the g factor. The obtained Zeeman relation with the pseudogap temperature T^⋆, g^∥cμ_BH_pg^∥c=g^∥abμ_BH_pg^∥ab≈k_BT^⋆, is fully consistent with the correlations only in the spin channel.