Electronic structure of electron-dopedSm1.86Ce0.14CuO4: Strong pseudogap effects, nodeless gap, and signatures of short-range order

Abstract

Angle-resolved photoemission spectroscopy (ARPES) data from the electron-doped cuprate superconductor ${\mathrm{Sm}}_{1.86}{\mathrm{Ce}}_{0.14}\mathrm{Cu}{\mathrm{O}}_{4}$ show a much stronger pseudogap or hot-spot effect than that observed in other optimally doped $n$-type cuprates. Importantly, these effects are strong enough to drive the zone-diagonal states below the chemical potential, implying that $d$-wave superconductivity in this compound would be of the nodeless gap variety. The gross features of the Fermi surface topology and low-energy electronic structure are found to be well described by reconstruction of bands by a $\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2}$ order. Comparison of the ARPES and optical data from the same sample shows that the pseudogap energy observed in optical data is consistent with the interband transition energy of the model, allowing us to have a unified picture of pseudogap effects. However, the high-energy electronic structure is found to be inconsistent with such a scenario. We show that a number of these model inconsistencies can be resolved by considering a short-range ordering or inhomogeneous state.