Thinning
crystalline materials to two dimensions (2D) creates a
rich playground for electronic phases, including charge, spin, superconducting,
and topological order. Bulk materials hosting charge density waves
(CDWs), when reduced to ultrathin films, have shown CDW enhancement
and tunability. However, charge order confined to only 2D remains
elusive. Here we report a distinct charge ordered state emerging in
the monolayer limit of 1T-VSe2. Systematic
scanning tunneling microscopy experiments reveal that bilayer VSe2 largely retains the bulk electronic structure, hosting a
tridirectional CDW. However, monolayer VSe2 consistently
across distinct substratesexhibits a dimensional crossover,
hosting two CDWs with distinct wavelengths and transition temperatures.
Electronic structure calculations reveal that while one CDW is bulk-like
and arises from the well-known Peierls mechanism, the other is decidedly
unconventional. The observed CDW-lattice decoupling and the emergence
of a flat band suggest that the second CDW could arise from enhanced
electron–electron interactions in the 2D limit. These findings
establish monolayer–VSe2 as a host of coexisting
charge orders with distinct origins, and enable the tailoring of electronic
phenomena via emergent interactions in 2D materials.