Non-Linear Modes in Lithium Niobate Ferroelectrics with niobium antisite defects

TL;DR

This paper investigates the nonlinear vibrational modes in lithium niobate ferroelectrics with niobium antisite defects using a nonlinear Klein-Gordon model and multiple time-scale analysis, revealing detailed mode behaviors and frequency shifts.

Contribution

It introduces a detailed analysis of linear and nonlinear modes in lithium niobate with defects using a nonlinear Klein-Gordon framework and multiple time-scale analysis.

Findings

First three linear mode frequencies as a function of defect concentration.

Presence of nonlinear localized modes (ILMs) in the system.

External harmonic excitation does not guarantee phase-locking of even modes.

Abstract

Ferroelectric belongs to an important class of materials showing very interesting nonlinear optical properties that have a variety of application in photonic devices In a discrete Hamiltonian, if we consider the space and time dependence of polarization vectors with an interaction term between two polarization domains, it gives rise to a nonlinear Klein-Gordon (K-G) equation that has been shown in some systems [1]. This equation as a governing equation enables multiple time-scale analysis (MTSA) to be performed on a real ferroelectric material that reveals new type of information on both linear (known as soft modes) and the nonlinear parts of frequencies and amplitudes of oscillations. MTSA was described in a K-G system based on staggered polarization where more emphasis was given to reveal the presence of intrinsic localized modes (ILM). Here, detailed results for the first three linear modes and their frequencies as a 2 function of a wide range of niobium antisite defects or, impurities in lithium niobate ferroelectric are presented. It is found that when an external excitation (i.e. the input) is only harmonic in nature, it could not be ascertained whether the even modes of the solitonic waves (i.e. the output) will have phase-locking with this type of harmonic external force.