Large-gap insulating dimer ground state in monolayer IrTe₂

Monolayer (ML) of two-dimensional van der Waals (vdW) materials exhibit novel electronic phases distinct from their bulk due to the absence of interlayer coupling and the resulting electronic structure and symmetry changes. Here, by a combined study of angle-resolved photoemission spectroscopy and scanning tunneling microscopy/spectroscopy, we report the emergence of unique 2 x 1 insulating Ir dimerized ground state in monolayer IrTe₂ with a larger than 1 eV band gap, which is distinct from the metallic bilayer (BL) and bulk. First-principle calculations reveal that the strong Te-Te interlayer coupling plays a vital role in IrTe₂ layer resulting in the large-gap metal-to-insulator transition, when the thickness changes from BL to ML, by strongly affecting the charge and phonon properties. Our findings provide compelling case of an emergent novel ground state caused by the strong interlayer coupling in vdW layered materials and its absence in the monolayer.