Giant Optomechanical Coupling in the Charge Density Wave State of Tantalum Disulfide

TL;DR

This paper demonstrates giant optomechanical coupling in the charge density wave state of Tantalum Disulfide, showing potential for advanced non-linear optical applications through light-induced control of structural dynamics.

Contribution

It reveals exceptionally large dielectric changes and optomechanical coupling in $1T$-$ ext{TaS}_2$, and develops a model matching experimental results for light-induced structural dynamics.

Findings

Dielectric function changes significantly along the amplitude mode.

Optomechanical coupling coefficients are two orders of magnitude larger than diamond.

Light-induced structural dynamics can be controlled to enhance non-linear optical responses.

Abstract

We study the coupling of light and the structural order parameter in the charge density wave (CDW) state of the layered transition-metal dichalcogenide, Tantalum Disulfide ($1T-\mathrm{TaS_2}$). Using time-dependent density functional theory calculations of the dielectric properties along the distortions coordinates, we show that $1T-\mathrm{TaS_2}$ displays very large change in its dielectric function along the amplitude (Higgs) mode due to the coupling of the periodic lattice distortion with an in-plane metal-insulator transition, leading to optomechanical coupling coefficients two orders of magnitude larger than the ones of diamond and ErFeO$_3$. In addition, we derive an effective model of the light-induced dynamics, which is in quantitative agreement with experimental observations in $1T-\mathrm{TaS_2}$. We show that light-induced dynamics of the structural order parameter in $1T-\mathrm{TaS_2}$ can be deterministically controlled to engineer large third-order non-linear optical susceptibilities. Our findings suggest that CDW materials are promising active materials for non-linear optics.