Multiple quantum confinement effects in charge density wave nanostructures

Confining charge carriers of materials into a geometrical configuration is expected to destabilize their intrinsic ground electronic states. Especially for the many-body interacting systems, understanding the underlying physics of quantum confined behaviors at the atomic scale is critical for the advancement of nanoscience and nanotechnology. Here we report scanning tunneling microscopy experiments on anomalous quantum confinement effects in triangularlike nanostructures of monolayer H-NbSe2, a prototypical two-dimensional (2D) charge-density-wave (CDW) metal, as well as their modulation by substrate engineering. Domain boundaries usually appear in monolayer H-NbSe2 nanostructures as they are directly placed onto graphene, while they are absent with insertion of a metallic H-NbSe2 or insulating T-NbSe2 monolayer. Moreover, both H-NbSe2 and T-NbSe2 substrates can effectively induce striped charge states in H-NbSe2 nanostructures. Our spectroscopic measurements further reveal unique electron confinements in monolayer H-NbSe2 nanostructures on H-NbSe2 substrates, where the confined electrons can be visualized either along the nanostructure edges or within the nanostructures, dependent on the electron energies. Our results provide a fruitful playground for investigating the intertwined quantum confinement effects in CDW nanostructures under the 2D limit.