Evidence of Surface Interlayer Dimerization in the Commensurate Charge Density Wave Phase of 1T-TaSe2

Van der Waals layered materials offer unprecedented opportunities to tune electronic properties by controlling, for instance, the number of layers or their mutual twist angle. However, the translational degree of freedom has not been given proportionate attention. Within the wide family of transition metal dichalcogenides, the commensurate charge density wave (CCDW) phase of 1T-TaSe2 is predicted to host several quantum states ranging from 1D metal to 3D insulator depending on the lateral stacking. By means of angle-resolved photoemission spectroscopy with micrometer spatial resolution, we studied the charge-ordered 1T-TaSe2, revealing the coexistence of metallic and insulating surface domains. Our investigation clarifies that metallicity is due to a specific lateral sliding of the CCDW layers, while insulating behavior is driven by surface interlayer dimerization. These results open intriguing potentialities in surface functionalization and control of electronic structure.