Cavity magnon-polaritons in cuprate parent compounds

TL;DR

This paper proposes a method to couple Terahertz cavities with antiferromagnetic fluctuations in cuprates, leading to hybrid magnon-polaritons and bimagnon interactions, with potential applications in manipulating high-temperature superconductors.

Contribution

It introduces a novel coupling scheme between cavity fields and magnetic excitations in cuprates, including a linear hybridization and a higher-order bimagnon interaction, expanding the understanding of cavity-matter interactions in strongly correlated systems.

Findings

Hybrid magnon-polaritons form via cavity-magnon coupling.

Bimagnon-cavity interaction is strong but heavily damped.

Asymmetric cavity line-shapes observed in strong coupling regime.

Abstract

Cavity control of quantum matter may offer new ways to study and manipulate many-body systems. A particularly appealing idea is to use cavities to enhance superconductivity, especially in unconventional or high-$T_c$ systems. Motivated by this, we propose a scheme for coupling Terahertz resonators to the antiferromagnetic fluctuations in a cuprate parent compound, which are believed to provide the glue for Cooper pairs in the superconducting phase. First, we derive the interaction between magnon excitations of the Ne\'el-order and polar phonons associated with the planar oxygens. This mode also couples to the cavity electric field, and in the presence of spin-orbit interactions mediates a linear coupling between the cavity and magnons, forming hybridized magnon-polaritons. This hybridization vanishes linearly with photon momentum, implying the need for near-field optical methods, which we analyze within a simple model. We then derive a higher-order coupling between the cavity and magnons which is only present in bilayer systems, but does not rely on spin-orbit coupling. This interaction is found to be large, but only couples to the bimagnon operator. As a result we find a strong, but heavily damped, bimagnon-cavity interaction which produces highly asymmetric cavity line-shapes in the strong-coupling regime. To conclude, we outline several interesting extensions of our theory, including applications to carrier-doped cuprates and other strongly-correlated systems with Terahertz-scale magnetic excitations.