Strong and controlled photonic spin Hall effect in a van der Waals semiconducting transition metal oxide slab

Abstract

A natural biaxial van der Waals material α-MoO3 hosts the in-plane anisotropy as well as the ultra-low-loss polaritons, which hold great potential in the applications of subwavelength focusing, planar nanooptics as well as polarization converters. Here, we show that the simple α-MoO3 slab supports giant spin shifts of the reflected wave for either the horizontal (H) or vertical (V) polarized incident waves at specific frequencies and the low as well as large incident angle regions, whose maximum values can reach their theoretical upper limit. Such obtained giant spin shifts at the low and large incident angles are governed by the intrinsically in-plane anisotropy of α-MoO3 and the zero values of the reflectance at the transverse magnetic or electric wave. In addition, we also examine how the orientation of the optical axis of α-MoO3 slab controls the sign and magnitude of the reflected spin shifts and find that the positions where the maximum spin shifts of the reflected wave happen can be switched by rotating it. Our results on the reflected spin shifts in the α-MoO3 slab lay a foundation for unraveling the photonic spin Hall effects of anisotropic van der Waals crystals.