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 Bi2Sr 2CaCu2O8+y, over a wide range of hole doping (0.10 ≤ p ≤ 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* are related via a Zeeman relation gμB Hpg≈ k BT*, 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.