Optical Tunable MoiréExcitons in Twisted Hexagonal GaTe Bilayers

Optical fine-tunable layer-hybridized Moiréexcitons are highly in demand for emerging many-body states in two-dimensional semiconductors.We report naturally confined layer-hybridized bright Moiréexcitons with long lifetimes in twisted hexagonal GaTe bilayers,using ab initio many-body perturbation theory and the Bethe–Salpeter equation.Due to the hybridization of electrons and holes between layers,which enhances the brightness of excitons,the twisted bilayer system becomes attractive for optical applications.We find that in both R and H-type stacking Moirésuperlattices,more than 200 meV lateral quantum confinements occur on exciton energies,which results in two scenarios:(1)The ground state bright excitons XA are found to be trapped at two high-symmetry points,with opposite electric dipoles in the R-stacking Moirésupercell,forming a honeycomb superlattice of nearest-neighbor dipolar attraction.(2)For H-stacking case,the XA is found to be trapped at only one high-symmetry point exhibiting a triangular superlattice.Our results suggest that twisted h-GaTe bilayer is one of the promising systems for optical fine-tunable excitonic devices and provide an ideal platform for realizing strong correlated Bose–Hubbard physics.

Efficient terahertz generation from van der Waalsα-In_(2)Se_(3)

Two-dimensional(2D)van der Waals materials have attracted tremendous attention due to their versatile physical properties and flexible manipulation approaches.Among the various types of van der Waals materials,α-In_(2)Se_(3)is remarkable for its intrinsic 2D ferroelectricity and high-performance opto-electronic properties.However,the study of theα-In_(2)Se_(3)system in terahertz(THz)radiation is scarce,although it is promising for electrically controlled THz field manipulation.We investigate theα-In_(2)Se_(3)in different thicknesses and report that the THz generation efficiency induced by femtosecond laser pulses can be largely improved by reducing the thickness from the bulk.Furthermore,we reveal the surge current in thin film coupled with THz emission exhibits a different Auger recombination mode,which is helpful in understanding the mechanism and provides insights into the design of 2D highly efficient THz devices.