Dimensionality reduction and band quantization induced by potassium intercalation in 1T−HfTe2

We have performed angle-resolved photoemission spectroscopy on transition-metal dichalcogenide $1T\text{\ensuremath{-}}{\mathrm{HfTe}}_{2}$ to elucidate the evolution of electronic states upon potassium (K) deposition. In pristine ${\mathrm{HfTe}}_{2}$, an in-plane hole pocket and electron pockets are observed at the Brillouin-zone center and corner, respectively, indicating the semimetallic nature of bulk ${\mathrm{HfTe}}_{2}$, with dispersion perpendicular to the plane. In contrast, the band structure of heavily K-dosed ${\mathrm{HfTe}}_{2}$ is obviously different from that of bulk and resembles the band structure calculated for monolayer ${\mathrm{HfTe}}_{2}$. It was also observed that lightly K-dosed ${\mathrm{HfTe}}_{2}$ is characterized by quantized bands originating from bilayer and trilayer ${\mathrm{HfTe}}_{2}$, 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.