Coulomb-oscillator explanation of striped STM images of superconductive copper oxides

TL;DR

This paper explains the striped STM images of superconductive copper oxides using a Coulomb-oscillator model, linking ion displacements to electron pathways and superconductivity.

Contribution

It introduces a Coulomb-oscillator explanation for STM images, connecting ion displacement patterns to electron oscillations and superconductivity in copper oxides.

Findings

Ion displacements create superlattice structures.

Ladder patterns correspond to Coulomb oscillators.

Pathways for 3s electrons account for superconductivity.

Abstract

Asymmetric scanning tunneling microscopy (STM) of the CuO2 plane of Ca2-xNaxCuO2Cl2, x = 0.125, shows a square domain structure with edge length four times the compound's lattice constant a0 (Cu-O-Cu distance). The domain structure is a direct consequence of the 4a0 by 4a0 superlattice formed by vertical Na+ pairs (oriented parallel to the crystal's c axis) that substitute Ca2+ ions. The surrounding O2- ions are displaced away from, and the Cu2+ ions toward the Na+ pairs. Contrary to the fourfold symmetry of the CuO2 plane, the stable displacement configuration has a twofold symmetry, dominated by large and, respectively, small displacement of opposite O2- ions being nearest neighbors to each vertical Na+ pair. The ion displacements give rise to sufficient squeeze of certain O2- ions that, by the Coulomb-oscillator model of superconductivity, prevents lateral overswing of their excited 3s electrons. The axial 3s oscillations are predominantly oriented in the directions of O2- ion displacements. The observed ladder pattern in the domains provides a direct imaging of the 3s Coulomb oscillators. The 'sidepieces' of the ladders correspond to long unidirectional pathways for 3s electrons in the CuO2 plane. They account for superconductivity. The findings lend support to the validity of the Coulomb-oscillator model of superconductivity.