  Excitons in van der Waals (vdW) stacking interfaces can be trapped in ordered
moire potential arrays giving rise to attractive phenomenons of quantum optics
and bosonic many-body effects. Compare to the prevalent transition metal
dichalcogenides (TMDs) systems, due to the wide bandgap and low dielectric
constant, excitons in twist-stacked hexagonal boron nitride (hBN) are
anticipated trapped in deeper moire potential, which enhances the strength of
interactions. However, constrained by the common low detectivity of weak
light-emitting in the deep-ultraviolet (DUV) bands, the moire excitons in
twisthBN remain elusive. Here, we report that a remarkable DUV emitting band
(peak located at ~260 nm) only emerges at the twisted stacking area of hBN,
which is performed by a high collection efficiency and spatially-resolved
cathodoluminescence (CL) at room temperature. Significant peak redshifting
contrast to defect-bound excitons of bulk hBN indicates the giant trapping
effects of moir\'e potential for excitons. The observation of deeply trapped
excitons motivates further studies of bosonic strongly correlation physics
based on the twist-hBN system.
