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

In high temperature (high T c ) cuprate superconductors the gap in the electronic density of states is not fully filled at T c ; it evolves into a partial (pseudo)gap that survives way beyond T c , challenging the conventional views. We have investigated the pseudogap phenomenon in the field-temperature (H-T) diagram of Bi 2 Sr 2 CaCu 2 O 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 H pg . We found that H pg and the pseudogap onset temperature T * are related via a Zeeman relation $g\mu_BH_{pg} \approx k_BT^*$ , irrespective of whether the magnetic field is applied along the c-axis or parallel to CuO 2 planes. In contrast to large anisotropy of the superconducting state, the field anisotropy of H pg 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. Copyright Springer-Verlag Berlin/Heidelberg 2004