Switching of charge-density wave by carrier tuning in monolayer TiTe2

How charge-density wave (CDW) is influenced by the change in the dimensionality is a fundamental question in condensed-matter physics. Monolayer titanium ditelluride (TiTe2) undergoes 2×2 CDW despite the absence of CDW in the bulk counterpart, whereas the mechanism of CDW is under intensive debate. Here we show that the CDW of monolayer TiTe2 can be conveniently switched by carrier tuning via controlling the Te ratio during molecular-beam epitaxy or depositing potassium (K) atoms on the surface. This is demonstrated by monitoring the CDW-induced 2×2 band folding using angle-resolved photoemission spectroscopy. Remarkably, the CDW appears only when the inner hole pocket at the Γ point and the elongated electron pocket at the M point show partial Fermi-surface nesting. The present study suggests that the carrier doping is an effective method to pin down the mechanism of CDW in atomic-layer transition-metal dichalcogenides.