Electronic Structure of Electron-doped Sm1.86Ce0.14CuO4: Strong `Pseudo-Gap' Effects, Nodeless Gap and Signatures of Short Range Order

TL;DR

This study uses ARPES to reveal strong pseudo-gap effects and a nodeless superconducting gap in electron-doped Sm1.86Ce0.14CuO4, suggesting a complex interplay of band reconstruction and short-range order.

Contribution

It provides a detailed analysis of pseudo-gap phenomena and electronic structure in electron-doped cuprates, highlighting the role of short-range order and band reconstruction.

Findings

Pseudo-gap effects are stronger than in other n-type cuprates.

Zone-diagonal states are driven below the chemical potential, indicating a nodeless gap.

Band reconstruction by a $\sqrt{2} imes\sqrt{2}$ order explains Fermi surface features.

Abstract

Angle resolved photoemission (ARPES) data from the electron doped cuprate superconductor Sm$_{1.86}$Ce$_{0.14}$CuO$_4$ shows a much stronger pseudo-gap 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 a novel "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 $\sqrt{2}\times\sqrt{2}$ order. Comparison of the ARPES and optical data from the $same$ sample shows that the pseudo-gap energy observed in optical data is consistent with the inter-band transition energy of the model, allowing us to have a unified picture of pseudo-gap 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.