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

In high temperature (high T <Subscript> c </Subscript>) cuprate superconductors the gap in the electronic density of states is not fully filled at T <Subscript> c </Subscript>; it evolves into a partial (pseudo)gap that survives way beyond T <Subscript> c </Subscript>, challenging the conventional views. We have investigated the pseudogap phenomenon in the field-temperature (H-T) diagram of Bi<Subscript>2</Subscript>Sr<Subscript>2</Subscript>CaCu<Subscript>2</Subs cript>O<Subscript>8 + y </Subscript> over a wide range of hole doping (<InlineEquation ID="Equ1"> <EquationSource Format="TEX">$0.10 \leq p \leq 0.225$</EquationSource> </InlineEquation>). 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 <Subscript> pg </Subscript>. We found that H <Subscript> pg </Subscript> and the pseudogap onset temperature T <Superscript>*</Superscript> are related via a Zeeman relation <InlineEquation ID="Equ2"> <EquationSource Format="TEX">$g\mu_BH_{pg} \approx k_BT^*$</EquationSource> </InlineEquation>, irrespective of whether the magnetic field is applied along the c-axis or parallel to CuO<Subscript>2</Subscript> planes. In contrast to large anisotropy of the superconducting state, the field anisotropy of H <Subscript> pg </Subscript> 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