UC Berkeley

The spontaneous formation of electronic orders is a crucial element for understanding complex quantum states and engineering heterostructures in 2D materials. A novel 19 $\sqrt {19} $ × 19 $\sqrt {19} $ charge order in few-layer-thick 1T-TaTe₂ transition metal dichalcogenide films grown by molecular beam epitaxy, which has not been realized, is report. The photoemission and scanning probe measurements demonstrate that monolayer 1T-TaTe₂ exhibits a variety of metastable charge density wave orders, including the 19 $\sqrt {19} $ × 19 $\sqrt {19} $ superstructure, which can be selectively stabilized by controlling the post-growth annealing temperature. Moreover, it is found that only the 19 $\sqrt {19} $ × 19 $\sqrt {19} $ order persists in 1T-TaTe₂ films thicker than a monolayer, up to 8 layers. The findings identify the previously unrealized novel electronic order in a much-studied transition metal dichalcogenide and provide a viable route to control it within the epitaxial growth process.