Proposed Chiral Texture of the Magnetic Moments of Unit-Cell Loop Currents in the Pseudogap Phase of Cuprate Superconductors

TL;DR

This paper introduces a new chiral order parameter based on a helical loop-current structure to explain the polar Kerr effect observed in the pseudogap phase of cuprate superconductors, linking magnetoelectric effects to optical gyrotropy.

Contribution

It proposes a novel helical loop-current model that breaks inversion symmetry and accounts for the polar Kerr effect in underdoped cuprates, extending the loop-current framework.

Findings

Helical loop-current structure induces optical gyrotropy.

Coupling between layers produces circular dichroism.

Model explains the polar Kerr effect in cuprates.

Abstract

We propose a novel chiral order parameter to explain the unusual polar Kerr effect in underdoped cuprates. It is based on the loop-current model by Varma, which is characterized by the in-plane anapole moment N and exhibits the magnetoelectric effect. We propose a helical structure where the vector N^(n) in the layer n is twisted by the angle pi/2 relative to N^(n-1), thus breaking inversion symmetry. We show that coupling between magnetoelectric terms in the neighboring layers for this structure produces optical gyrotropy, which results in circular dichroism and the polar Kerr effect.