Rotational Symmetry Breaking in Sodium Doped Cuprates

TL;DR

This paper explains the observed local rotational symmetry breaking in sodium-doped cuprates by analyzing the anisotropic conductance patterns caused by hole states bound to Na+ acceptors, aligning with recent experimental findings.

Contribution

It introduces a theoretical model showing how a doubly degenerate hole bound state causes anisotropic conductance patterns, explaining symmetry breaking in cuprates.

Findings

Doubly degenerate ground state causes anisotropic conductance.

Anisotropy varies with voltage, being more pronounced at lower voltages.

Qualitative agreement with recent experimental observations.

Abstract

For reasonable parameters a hole bound to a Na^{+} acceptor in Ca_{2-x}Na_{x}CuO_{2}Cl_{2} has a doubly degenerate ground state whose components can be represented as states with even (odd) reflection symmetry around the x(y) -axes. The conductance pattern for one state is anisotropic as the tip of a tunneling microscope scans above the Cu-O-Cu bonds along the x(y)-axes. This anisotropy is pronounced at lower voltages but is reduced at higher voltages. Qualitative agreement with recent experiments leads us to propose this effect as an explanation of the broken local rotational symmetry.