Suppression of the antiferromagnetic pseudogap in the electron-doped high-temperature superconductor by "protect annealing"

TL;DR

This study demonstrates that protect annealing in electron-doped cuprates suppresses antiferromagnetic pseudogap, leading to a more uniform superconducting state with a wider doping range, fundamentally altering the understanding of their electronic structure.

Contribution

The paper introduces a protect annealing method that significantly reduces AFM correlations in electron-doped cuprates, revealing a uniform superconducting state across a broad doping range.

Findings

Absence of AFM pseudogap in ARPES measurements

Superconductivity extends over a wide electron concentration range

Dramatic reduction of AFM correlation length and magnetic moments

Abstract

In the hole-doped cuprates, a small amount of carriers suppresses antiferromagnetism and induces superconductivity. In the electron-doped cuprates, on the other hand, superconductivity appears only in a narrow range of high electron concentration ($\sim$ doped Ce content) after reduction annealing, and strong antiferromagnetic (AFM) correlation persists in the superconducting phase. Recently, Pr$_{1.3-x}$La$_{0.7}$Ce$_{x}$CuO$_{4}$ (PLCCO) bulk single crystals annealed by a "protect annealing" method showed a high $T_c$ of $\sim$ 27 K for small Ce content down to $x \sim 0.05$. By angle-resolved photoemission spectroscopy (ARPES) measurements of PLCCO crystals, we observed a sharp quasi-particle peak on the entire Fermi surface without signature of an AFM pseudogap unlike all the previous work, indicating a dramatic reduction of AFM correlation length and/or of magnetic moments. The superconducting state was found to extend over a wide electron concentration range. The present ARPES results fundamentally change the long-standing picture on the electronic structure in the electron-doped regime.