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.
Highlights
Using light to control the properties of quantum materials holds the potential to realize new and interesting quantum many-body phases [1–16] but may hold the key to create novel devices and functionalities [17–29]
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
This coupling yields an effective magnetoelectric coupling which is linear in electric field but quadratic in the spin waves. While this coupling doesn’t lead to the formation of polaritons, we show that, this does lead to a strong coupling between the photons and cavity, and may be promising in the future since it more naturally allows for controlling the correlations which are moderated by the spin-waves [67,179–184]
Summary
Using light to control the properties of quantum materials holds the potential to realize new and interesting quantum many-body phases [1–16] but may hold the key to create novel devices and functionalities [17–29]. It has been proposed that strongly coupling resonant cavities to infrared-active optical phonons [97–100] may offer a way to manipulate the pairing between electrons in conventional superconductors While this may be a promising avenue [79] toward achieving cavity-enhanced superconductivity, these systems still remain fundamentally limited by the relatively weak coupling strengths afforded by electronphonon interaction. We propose two suitable microscopic mechanisms by which magnons in the insulating cuprate may be coupled to cavity photons, which are organized into two main parts of this paper Both of these employ an infrared-active phonon mode [57] as an intermediary between the electric field of the cavity and the electron spins.
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