Giant and tunable photonic spin Hall effect in a parity-time symmetric structure with a Dirac semimetal material

The optical parity-time (PT) symmetry structure can yield unique properties, including periodicity, discreteness, nonlinearity, and so on. However, the component materials in these PT symmetry structures have been primarily restricted by their lack of tunability. Here, by utilizing the external stimulus-dependent optical properties of the Dirac semimetal, we report the theoretical prediction of the large and controllable photonic spin Hall effect in the PT symmetry structure with the slab of the Dirac semimetal. We provide evidence that the PT symmetry structure with the Dirac semimetal exhibits a large spin shift as high as the half of the waist at a certain incident angle, which is the conventionally theoretical upper limit. Due to the exceptional points, the spin shift can be enhanced effectively. Furthermore, we unravel that a small change in the Fermi energy of the Dirac semimetal on the order of 0.01 eV is able to engineer both the magnitude and sign of the spin shift. In particular, there is a transition in the spectrum of the spin shift when we vary the Fermi energy of the Dirac semimetal, where the number of the spin shift peak changes from one to two. Our results reveal the interplay between the light and the PT symmetry structure with the Dirac semimetal, which offers the possibility of developing Dirac semimetal-based spin-dependent photonic devices.