Effect of C3v symmetry breaking on the noncentrosymmetric quantum spin Hall insulating phase and optical characteristics of monolayer PbBiI

Abstract

Due to the rise of applications in several optoelectronic and spintronic platforms, theoretically engineering the propagation of light in low-dimensional systems dealing with both charge and spin degrees of freedom has recently triggered considerable interest. By breaking the ${C}_{3v}$ symmetry through external exchange fields, we engineer the propagation of an incident circularly polarized light in a noncentrosymmetric quantum spin Hall insulator, monolayer PbBiI, that is active in the near-infrared region of the electromagnetic spectrum. The Kubo formalism is ideal for optical properties. We endeavor to thoroughly demonstrate that a critical-breaking regime of three types of fields leads to various anisotropic electronic phases and optical interband transitions. We find various near-to-far infrared shifts for the optical activity of the system when the ${C}_{3v}$ symmetry breaking fields are turned on. This is proven in the ensuing two ways: The spectrum of optical conductivity components and the intensities of scattered/absorbed light. We further find the criteria under which the system is transparent. Finally, depending on the exchange fields, we engineer the eccentricities for the reflected and transmitted lights in monolayer PbBiI to see how the polarization of incident circular light becomes linear and elliptical. The applicability of results in industry and medicine is also briefly discussed.