Anisotropic terahertz optostriction in group-IV monochalcogenide compounds

Terahertz (THz) technology is a cutting-edge scheme with various promising applications, such as next generation telecommunication, nondestructive evaluation, security check, and in-depth characterization, owing to its sensitivity to material geometric change and good transparency. Even though tremendous progress has 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 optomechanical 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.