Changes of electronic structure across the insulator-to-metal transition of quasi-two-dimensional Na-intercalated β-HfNCl studied by photoemission and x-ray absorption

We use photoemission (PE) and x-ray absorption (XA) spectroscopy to study intercalation-induced changes in the electronic structure of β-HfNCl and (formula presented) PE shows appearance of new states in (formula presented) within the gap of β-HfNCl, with negligible changes in the energy positions of valence-band features of the parent, suggesting a non-rigid-band behavior. N (formula presented) XA results show that the tail of the conduction band, with a quasi-two-dimensional character, extends to lower energy in (formula presented) than in β-HfNCl. The study provides information on the electronic structure and its change across the insulator-to-metal transition of the new class of superconductors.