Mechanism of strain-modulated photonic spin Hall effect in Td-WTe2

Abstract

Weyl semimetals (WSMs) provide a promising platform for exploring strain modulation of the photonic spin Hall effect (PSHE) because of their topologically nontrivial band structures and strongly anisotropic optical responses. To clarify how strain modulates the PSHE through the optical response of WSMs, a first-principles-based strain–optical conductivity–PSHE framework was established, and a non-contact strain-measurement PSHE-based scheme was proposed. For this purpose, the type-II WSM Td-WTe2 was chosen as the study object, and density functional theory, Wannier interpolation, and the linear-response Kubo formalism were integrated to analyze the complex optical conductivity tensor, the Fresnel coefficients, and the resulting photonic spin Hall displacement. Under monochromatic illumination, the dependence of the photonic spin Hall displacement on incident angle and uniaxial strain was obtained by scanning incident angles from 30° to 90° and strains from −5% to +5%. The calculations showed that introducing Td-WTe2 at the reflection interface gave rise to a pronounced peak–valley pair within a narrow angular range. The angular positions of these features remained nearly unchanged, whereas their amplitudes varied systematically with strain. The strain-modulation mechanism was clarified by tracing the strain-dependent evolution of the conductivity tensor and its transfer, through the Fresnel response, to the photonic spin Hall displacement. Based on this relation, strain was quantitatively retrieved from the photonic spin Hall displacement measured at a fixed incident angle. This scheme provided a physics-based solution for optical strain analysis and measurement in anisotropic WSMs.