Electronic States and Excitation Spectra of Copper Oxides with Ladder and/or Chain

TL;DR

This paper investigates the electronic states and excitation spectra of copper oxides with ladder and chain structures, revealing hole transfer mechanisms and electronic interactions relevant to superconductivity.

Contribution

It provides a detailed analysis of hole distribution and electronic states in copper oxides, deriving an effective Hamiltonian and discussing magnetic interactions based on structural parameters.

Findings

Holes transfer from chains to ladders with Ca substitution

Derived effective Hamiltonian for edge-sharing chains

Discussed magnetic interactions and hopping energies dependence

Abstract

Recently the superconductivity has been reported in the copper oxides (Sr,Ca)$_{14}$Cu$_{24}$O$_{41}$ with ladders and edge-sharing chains under pressure. In order to understand the mechanism of the superconductivity, it is crucial to clarify the distribution of self-doped holes. From the analysis of the optical conductivity by ionic model and exact diagonalization method, we confirm that with substituting Ca for Sr, the self-doped holes are transferred from the chains to the ladders. We also examine the electronic states of edge-sharing chain in a variety of copper oxides, and derive the effective Hamiltonian. The dependences of the magnetic interactions between Cu ions and of the hopping energies of the Zhang-Rice singlet on the bond angle of Cu-O-Cu are discussed.