  Terahertz (THz) technology is a cutting-edge scheme with various promising
applications, such as next generation telecommunication, non-destructive
evaluation, security check, and in-depth characterization, owing to their
sensitivity to material geometric change and good transparency. Even though
tremendous progresses have been made during the past decade, exploration the
mechanisms of THz-matter interaction microscopically is still in its infancy.
In this work, we use thermodynamic theory to show how THz illumination deforms
materials and use group-IV monochalcogenide compounds to illustrate it.
According to our first-principles density functional theory calculations, THz
light with intermediate intensity (~109 W/cm2) could yield elastic deformations
on the order of ~0.1%, depending on laser polarization direction. Large
anisotropic opto-mechanical responses are also revealed. Finally, we show that
such strain can be detected via measuring the layer-resolved shift current
under a probe light irradiation.
