Bulk and surface electronic states in the dosed semimetallic HfTe$\boldsymbol{_2}$

The dosing of layered materials with alkali metals has become a commonly used strategy in ARPES experiments. However, precisely what occurs under such conditions, both structurally and electronically, has remained a matter of debate. Here we perform a systematic study of 1T-HfTe$_2$, a prototypical semimetal of the transition metal dichalcogenide family. By utilizing photon energy-dependent angle-resolved photoemission spectroscopy (ARPES), we have investigated the electronic structure of this material as a function of Potassium (K) deposition. From the k$_z$ maps, we observe the appearance of 2D dispersive bands deriving from electron dosing, with an increasing sharpness of the bands, consistent with the wavefunction confinement at the topmost layer. By bringing the topmost valence band below $E_F$, we can directly measure a band overlap of $\sim$ 0.2 eV. Accordingly, our shallow core level spectroscopy results show that a strong vertical field, concomitant with alkali metal dosing is the most compelling scenario to take place. However, 3D bulk-like states still contribute to the spectra even after considerable dosing. Our work provides a reference point for the increasingly popular studies of the alkali metal dosing of semimetals using ARPES.