Electrodynamics of Nearly-Ferroelectric Superconductors

TL;DR

This paper investigates the optical response of nearly ferroelectric superconductors, revealing unique frequency-dependent behaviors and predicting new optical anomalies due to the interplay of superconductivity and ferroelectricity.

Contribution

It introduces a theoretical framework for the optical response of NFE-SCs, highlighting novel frequency-dependent propagation regimes and predicting optical anomalies.

Findings

Meissner-like field extinction below a critical frequency

Dielectric-like propagation in the anomalous frequency region

Predicted optical transmission peaks below the soft mode frequency

Abstract

We report here the frequency-dependent optical response of a nearly ferroelectric superconductor (NFE-SC), like Na$_{x}$WO$_3$, or n-SrTiO$_3$. From $\omega =0$, up to a critical frequency $ \omega_{c1}$, Meissner-like field extinction occurs as in a usual superconductor. In the "anomalous" region $\omega_{c1}<\omega<\omega_{TO}$ (the TO frequency of the NFE) the field propagates as in a dielectric. For $\omega >\omega_{TO}$ Meissner damping recurrs, then at higher $\omega$, dielectriclike propagation is found. New optical anomalies (peaks in transmission) are predicted for a film of NFE-SC below the soft mode frequency $\omega_{TO}$. These effects are due to including the contribution of the NFE displacement current in the solution of the coupled Maxwell, lattice and London equations. Quantitative calculations are given for the NFE-SC n-SrTiO$_3 $ to illustrate this.