Considerations on the symmetry of loop order in cuprates

TL;DR

This paper examines the symmetry properties of the loop-current order in cuprates' pseudogap phase, analyzing magnetic structures and related effects, with implications for experimental detection.

Contribution

It provides a detailed analysis of the lattice point group symmetry of the magnetic structure associated with loop-current order in cuprates.

Findings

Magnetic effects are small and difficult to observe experimentally.

Electronic energy effects related to the order are significantly larger.

Symmetry considerations influence observable physical phenomena.

Abstract

The loop-current state discovered in the pseudogap phase of cuprates breaks time reversal symmetry and lowers the point group symmetry of the crystal. The order parameter and the magnetic structure within each unit cell which is associated with it can be described by a toroidal moment parallel to the copper-oxide planes. We discuss lattice point group symmetry of the magnetic structure. As an application, we discuss a few effects that necessarily accompany order parameter in the pseudogap phase. The magnitude estimated for these specific effects makes them hard to observe because they rely on the small magnetic fields associated with the order parameter. Effects, associated with the electronic energies are much larger. Some of them have already been discussed.