A Tale of Two Entangled Instabilities: Dual Role of delta-O in HgBa2Ca(n-1)Cu(n)O(2(n+1)+delta)

TL;DR

This paper investigates how oxygen intercalation influences the electronic structure and instabilities in cuprate superconductors, revealing a dual role of delta-O in modulating structural and electronic properties relevant to high-temperature superconductivity.

Contribution

It demonstrates, using supercell DFT, how oxygen intercalation alters buffer layer structures and pulls oxygen bands to the Fermi level, impacting superconductivity mechanisms.

Findings

Oxygen intercalation affects buffer layer structures.

Attenuated crystal field pulls oxygen bands to EF.

Validation shows qualitative agreement with experimental doping effects.

Abstract

Low-energy instabilities in the hole doped cuprates include, besides short range antiferromagnetic fluctuations and superconductivity, also ubiquitous translational and rotational symmetry breakings. The overwhelming majority of interpretations of these possibly related properties rely on mappings onto three bands spanned by the three atomic orbitals Cu3d(x2-y2)(sigma), O2px(sigma), and O2py(sigma), these three local orbitals spanning the Zhang-Rice band (ZRB), the lower Hubbard bands (LHB) and the upper Hubbard bands (UHB), respectively. Here we demonstrate by means of supercell Density Functional Theory (DFT) (a) how oxygen intercalation affects the structures of the buffer layers, and (b) how the attenuated crystal field pulls two additional oxygen bands in the CuO2 plane to the Fermi level. The self-consistent changes in electronic structure reflected in the corresponding changes in external potential comprise formal properties of the Hohenberg-Kohn theorems. Validation of present days' approximate exchange-correlation potentials to capture these qualitative effects by means of supercell DFT is made by comparing computed doping dependent structural shifts to corresponding experimentally observed correlations. The simplest generalization of Bardeen-Cooper-Schrieffer (BCS) theory is offered to articulate high critical temperature superconductivity (HTS) from a normal state where crystal field causes states related to two non-hybridizing bands to coalesce at EF.