Ferron-Polaritons in Superconductor/Ferroelectric/Superconductor Heterostructures

TL;DR

This work predicts ferron-polaritons in superconductor/ferroelectric/superconductor trilayers, arising from ultrastrong coupling between out-of-plane ferron excitations and Swihart photons. By solving Maxwell’s equations with depolarization-field feedback and quantizing both the ferron modes and Swihart mode, the authors derive an isotropic ferron–photon hybrid spectrum with a THz-scale gap that far exceeds magnetic analogues. The coupling is mediated by the depolarization field and is resonantly enhanced when the Swihart frequency matches the ferron frequency, yielding an ultrastrong regime with |g| comparable to system frequencies. The results establish S/FE/S structures as a versatile platform for exploring extreme light–matter coupling and ferrolectric-based quantum technologies at terahertz frequencies.

Abstract

We predict the formation of ferron-polariton - a hybrid light-matter quasiparticle arising from the coupling between collective ferroelectric excitations (ferrons) and Swihart photons in a superconductor/ferroelectric/superconductor heterostructure. The coupling provides direct evidence for ferrons and reaches the ultrastrong-coupling regime, with a spectral gap in the terahertz range, orders of magnitude larger than those in magnetic analogues, reflecting the superior strength of electric dipole interactions. Our work establishes superconductor-ferroelectric heterostructures as a novel platform for exploring extreme light-matter coupling and for developing high-speed, ferroelectric-based quantum technologies at terahertz frequencies.

Figures (2)

• Figure 1: Schematic of the S/FE/S heterostructure. The ferron mode polarized normal to the film interfaces, characterized by the polarization fluctuation $\delta \bm{p}_x$ (illustrated by the accompanying bound charges), couples to the in-plane-confined electric field $\bm{E}_{\rm Sw}$ of the Swihart photon mode in the superconducting resonator.
• Figure 2: Spectra of ferron-polariton and ferron excitations of the S/FE/S structure. $d_P/\lambda_{\rm eff}=1/8$, $\{\alpha_1,\alpha_2,\alpha_3\} = \{-2.012,3.608,1.345\}\times 10^9 \; \text{Nm/C}^2$, and $\Omega_p=6.39$ THz. The $\delta p_x$-ferron-polariton branches $\omega_{u,l}$ are shown by the blue curves. The $\delta p_x$-ferron dispersion $\omega_1$ in the limit $\lambda_{\rm eff} \to \infty$ is shown by the red curve. $\delta p_{y,z}$-ferron frequencies $\omega_\pm$, which are the same in the presence of the superconducting screening and at $\lambda_{\rm eff} \to \infty$, are shown by blue-red dashed curves.