Wide-range electrically tunable photonic spin Hall effect in a quasi-PT-symmetric structure

The photonic spin Hall effect (PSHE), manifesting itself as the spin-dependent shifts of left- and right-handed circularly polarized light beams, holds potential applications in nanophotonics and precision measurement. Thus, realizing effective enhancement and regulation of PSHE is highly desirable. It is known that by adjusting the Fermi energy of graphene, the spin shifts in a graphene-based optical structure can be actively modulated and amplified. However, this method generally works in a very narrow range of incident angles (near Brewster's angle) and the incident state is limited to the horizontal polarization. In this Letter, we address these issues by theoretically proposing a feasible way to amplify and control the PSHE in a wide range of incident angles by modulating the Fermi energy when the light beam is reflected at a quasi-PT-symmetric structure (gain-loss medium embedded with monolayer graphene). Interestingly, we reveal that the electrically tunable PSHE can be achieved for both horizontal and vertical polarizations near the quasi-exceptional points (quasi-EPs). Moreover, we can directly determine the tiny variation of the Fermi energy by observing the field distribution of a single circularly polarized component in this structure without using the weak measurements.