Field anisotropy of the pseudogap state in Bi₂Sr ₂CaCu₂O_8+y ultrahigh magnetic fields

The orientational anisotropy of the pseudogap closing field Hpg is investigated in magnetic fields up to 60 T applied parallel (∥ab) and normal (∥c) to CuO2 planes in Bi2Sr 2CaCu2O8+y. We find that, in contrast to large field anisotropy related to the orbital motion of Cooper pairs below the upper critical field Hc2, the temperature-independent and small anisotropy of Hpg is due to anisotropy of the g-factor: 9∥c/9 ∥ab = Hpg∥ab/Hpg∥c, indicating correlations only in the spin-channel.