Charge Instability in Single-Layer TiTe2 Mediated by van der Waals Bonding to Substrates

Single layers of transition metal dichalcogenides are of interest for emergent properties; an often-neglected issue is substrate effects. Our experiments show that the charge density wave in a single-layer TiTe2 grown on PtTe2 films is strongly suppressed by increasing the PtTe2 substrate thickness. Given that the interfacial bonding remains of the weak incommensurate van der Waals type, the observed changes are correlated with a thickness-dependent metallicity transformation in the PtTe2 substrate. The results illustrate the crucial role of the substrate in single-layer physics.