  Tuning dimensionality in van der Waals materials with finite interlayer
coupling has introduced various electronic phase transitions by conventional
mechanical exfoliation. Particularly when the electronic order is tied to the
modulation of the interlayer coupling, such dimensional tunability has a strong
impact on its stability and properties, which has rarely been investigated
experimentally. Here, we demonstrate a dimensional crossover of charge order in
IrTe$_2$ from genuine two- to quasi-three-dimension using low-temperature
scanning tunneling microscopy and spectroscopy. Employing atomically thin
IrTe$_2$ flakes ranging from monolayer to multilayer, we observe a gradual
phase transition of charge order and exponential decay of Coulomb gap with
increasing thickness. Moreover, we find a suppression of the density of states
emerging at an abrupt lateral interface between two- and three-dimension. These
findings are attributed to the interplay between the strongly coupled layers
and substrate-driven perturbation, which can provide a new insight into the
dimensional crossover of strongly coupled layered materials with hidden
electronic phases.
