Revisiting the Charge-Density-Wave Superlattice of 1 T − TiSe 2

A number of intriguing phenomena, including exciton condensation, orbital ordering, and emergence of chirality, have been proposed to accompany charge-density-wave (CDW) formation in the layered transition metal dichalcogenide 1T-TiSe_{2}. Explaining these effects relies on knowledge of the atomic displacement pattern underlying the CDW, yet structural proposals based on spatially averaging bulk crystal diffraction and surface-dependent scanning tunneling microscopy have remained inconsistent. Here, we revisit the CDW superlattice structure of 1T-TiSe_{2} with selected-area electron diffraction, a bulk-sensitive probe capable of capturing submicrometer spatial variations while maintaining high momentum resolution. We observed superlattice peak extinction rules that are incompatible with previously reported atomic displacement patterns, and we found two categories of CDW phases characterized by distinct interlayer orderings. Our analysis identifies a set of possible superlattice structures consistent with the extinction rules, all featuring a one-dimensional displacement pattern for each atomic type and possessing a large number of nearly degenerate CDW domains. These findings shed light on the longstanding discrepancy in the low-temperature space group of 1T-TiSe_{2} and provide a new basis for understanding the gyrotropic electronic order and metastability in this material. Our results further underscore the importance of bulk-sensitive mesoscopic techniques in investigating materials that host unconventional superlattices.