High-field interlayer tunnelling transport in layered cuprates: Uncovering the pseudogap state

In high temperature (high Tc) cuprate superconductors the gap in the electronic density of states is not fully filled at Tc; it evolves into a partial (pseudo)gap that survives way beyond Tc, challenging the conventional views. We have investigated the pseudogap phenomenon in the field-temperature ($H-T$) diagram of Bi2Sr2CaCu2O$_{8+y}$ over a wide range of hole doping ($0.10 \leq p \leq 0.225$). Using interlayer tunneling transport in magnetic fields up to 60 T to probe the density-of states (DOS) depletion at low excitation energies we mapped the pseudogap closing field Hpg. We found that Hpg and the pseudogap onset temperature $T^\star$ are related via a Zeeman relation $g\mu_BH_{pg} \approx k_BT^\star$, irrespective of whether the magnetic field is applied along the c-axis or parallel to CuO2 planes. In contrast to large anisotropy of the superconducting state, the field anisotropy of Hpg is due solely to the g-factor. Our findings indicate that the pseudogap is of singlet-spin origin, consistent with models based on doped Mott insulator