First principle prediction of structural distortions in the cuprates and their impact on the electronic structure

TL;DR

This paper uses density functional theory to accurately predict structural, electronic, and magnetic properties of cuprate superconductors, revealing the importance of structural distortions and spin fluctuations in understanding their complex behavior.

Contribution

It demonstrates how energy-lowering structural distortions can be incorporated into DFT to accurately describe cuprates' properties, including magnetic states and electronic structures, aligning with experimental data.

Findings

Accurate description of the AFM ground state of undoped cuprates.

Identification of low-energy competing spin and charge stripe orders.

Prediction of doped crystal structures matching STEM measurements.

Abstract

Materials-realistic microscopic theoretical descriptions of copper-based superconductors are challenging due to their complex crystal structures combined with strong electron interactions. Here, we demonstrate how density functional theory can accurately describe key structural, electronic, and magnetic properties of the normal state of the prototypical cuprate Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ (Bi-2212). We emphasize the importance of accounting for energy-lowering structural distortions, which then allows us to: (a) accurately describe the insulating antiferromagnetic (AFM) ground state of the undoped parent compound (in contrast to the metallic state predicted by previous {\it ab initio} studies); (b) identify numerous low-energy competing spin and charge stripe orders in the hole-overdoped material nearly degenerate in energy with the AFM ordered state, indicating strong spin fluctuations; (c) predict the lowest-energy hole-doped crystal structure including its long-range structural distortions and oxygen dopant positions that match high-resolution scanning transmission electron microscopy (STEM) measurements; and (d) describe electronic bands near the Fermi energy with flat antinodal dispersions and Fermi surfaces that in agreement with angle-resolved photoemission spectroscopy (ARPES) measurements and provide a clear explanation for the structural origins of the so-called ``shadow bands''. We also show how one must go beyond band theory and include fully dynamic spin fluctuations via a many-body approach when aiming to make quantitative predictions to measure the ARPES spectra in the overdoped material. Finally, regarding spatial inhomogeneity, we show that the local structure at the CuO$_2$ layer, rather than dopant electrostatic effects, modulates the local charge-transfer gaps, local correlation strengths, and by extension the local superconducting gaps.