Comment on "No Evidence for Orbital Loop Currents in Charge Ordered ${\rm YBa_2Cu_3O_{6+x}}$ from Polarized Neutron Diffraction"

TL;DR

This paper critically analyzes polarized neutron diffraction data, arguing that previous claims of no orbital loop currents in YBa2Cu3O6+x are due to detection limits, reaffirming the presence of intra-unit cell magnetic order in cuprates.

Contribution

It provides a detailed quantitative critique of Croft et al's experiment, supporting the persistence of intra-unit cell magnetic order in cuprates despite recent null results.

Findings

Croft et al's data falls below detection threshold

Previous experiments with larger samples detected magnetic order

The intra-unit cell order remains a universal feature in cuprates

Abstract

Intra-unit cell magnetic order has been observed in four different families of high-temperature superconductors from polarized neutron diffraction experiments and supported by several other techniques. That order, which does not break translation symmetry, is consistent with the predicted orbital moments generated by two microscopic loop currrents in each CuO$_2$ cell. Recently, using polarized neutron diffraction, Croft {\it et al} [Phys. Rev. B 96, 214504 (2017)] claim to find no evidence for such orbital loop currents in charge ordered ${\rm YBa_2Cu_3O_{6+x}}$. Their experiment is done with detwinned samples at least 100 times smaller than in previous experiments without counting much longer. We show by a detailed quantitative analysis of their data that contrary to their conclusion, the magnetic signal falls below their threshold of detection. None of the data reported by Croft {\it et al} challenge the universality of the intra-unit cell order in cuprates.