Implications of second harmonic generation for hidden order in Sr$_2$CuO$_2$Cl$_2$

TL;DR

This paper investigates the symmetry and magnetic order in Sr$_2$CuO$_2$Cl$_2$ using second harmonic generation data, proposing a revised magnetic point group that aligns with experimental observations and exploring potential ground states.

Contribution

The study re-evaluates the magnetic symmetry of SCOC based on second harmonic spectroscopy, suggesting a new magnetic point group consistent with experimental data.

Findings

Second harmonic spectroscopy indicates a magnetic point group $4/mm'm'$ in SCOC.

The proposed symmetry breaks certain mirror planes present in the original model.

Analysis of ground states compatible with the new symmetry.

Abstract

Sr$_2$CuO$_2$Cl$_2$ (SCOC) is a model undoped cuprate with $I4/mmm$ crystallographic symmetry, and a simple magnetic space group $C_Amca$ with associated magnetic point group $mmm1'$. However, recent second harmonic spectroscopy in the antiferromagnetic phase has challenged this picture, suggesting instead a magnetic point group $4/mm'm'$ that co-exists with the antiferromagnetism and breaks the two orthogonal mirror planes containing the tetragonal $c$-axis. Here, we analyze the symmetry of SCOC in light of the second harmonic results, and discuss possible ground states that are consistent with the data.