Soliton Generation in Negative Thermal Expansion Materials

Erin B Curry,Michael G Rozman,Jason N Hancock,Donal Sheets,Connor A Occhialini,Kaitlin Lyszak

doi:10.3389/fmats.2021.742195

Erin B Curry, Michael G Rozman + Show 4 more

Open Access

https://doi.org/10.3389/fmats.2021.742195

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Abstract

Strain solitons have been observed statically in several 2D materials and dynamically in substrate materials using ultrafast laser pulses. The latter case relies on lattice relaxation in response to ultrafast heating in a light-absorbing transducer material, a process which is sensitive to the thermal expansion coefficient. Here we consider an unusual case where the sign of the thermal expansion coefficient is negative, a scenario which is experimentally feasible in light of rapid and recent advances in the discovery of negative thermal expansion materials. We present numerical solutions to a nonlinear differential equation which has been repeatedly demonstrated to quantitatively model experimental data and discuss the salient results using realistic parameters for material linear and nonlinear elasticity. The solitons that emerge from the initial value problem with negative and positive thermal expansion are qualitatively different in several ways. The new case of negative thermal expansion gives rise to a nearly-periodic soliton train with chirped profile and free of an isolated shock front. We suggest this unanticipated result may be realized experimentally and assess the potential for certain applications of this generic effect.

Highlights

The propagation of strain waves through materials originating from an initial disturbance is of high interest to a variety of theoretical, experimental, and technological efforts
For the sake of exploring the physics of soliton evolution from negative thermal expansion (NTE) transducers, we assume the substrate would again be sapphire oriented along the 100 direction and we repeat the calculations of Figure 2 with η0 < 0 describing the initial strain pulse
We have provided the first assessment of the use of NTE materials as acousto-optic transducers for strain wave generation

Summary

Introduction

The propagation of strain waves through materials originating from an initial disturbance is of high interest to a variety of theoretical, experimental, and technological efforts. The resultant energy absorption, heating, and subsequent thermal expansion can generate a dynamic strain profile capable of propagating over macroscopic distances. Ultrafast laser experiments at low laser fluence (energy density) generated and subsequently detected acoustic strain pulses and related this observed sound propagation to the linear elastic properties of the propagation medium (Thomsen et al, 1984; Eesley et al, 1987; Wright, 1992). As experimentation with ultrafast lasers advanced, experiments were developed which are sensitive to the nonlinear elastic properties as well (Hao and Maris, 2001; Muskens, 2004). All such experiments have been performed on materials with positive thermal expansion (PTE)

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