We have performed angle-resolved photoemission spectroscopy on transition-metal dichalcogenide 1T-HfTe2 to elucidate the evolution of electronic states upon potassium (K) deposition. In pristine HfTe2, an in-plane hole pocket and electron pockets are observed at the Brillouin-zone center and corner, respectively, indicating the semimetallic nature of bulk HfTe2, with dispersion perpendicular to the plane. In contrast, the band structure of heavily K-dosed HfTe2 is obviously different from that of bulk and resembles the band structure calculated for monolayer HfTe2. It was also observed that lightly K-dosed HfTe2 is characterized by quantized bands originating from bilayer and trilayer HfTe2, indicative of staging. The results suggest that the dimensionality crossover from 3D (dimensional) to 2D electronic states due to systematic K intercalation takes place via staging in a single sample. The study provides a strategy for controlling the dimensionality and functionality of novel quantum materials.
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