Stress-induced multiple quantum phase transitions in the $B1$ and $B2$ phases of CeN

The quantum phase transition in Ce-based compounds has attracted significant attention in strongly correlated systems, primarily due to the dual nature of $f$ electrons. Rare-earth nitride (Re-N) compounds are particularly intriguing, as they exhibit major physical mechanisms such as the Kondo effect or mixed-valence behavior. Notably, CeN is anomalously small in lattice parameter compared with other Re-N compounds and there is a structure phase transition from $B\text{1-type}$ (NaCl-type) to $B2\text{−}\mathrm{type}$ (CsCl-type) at approximately 77 GPa. Hence, we study the electronic structures of $B\text{1-type}$ and $B2\text{−}\mathrm{type}$ CeN by tuning stress, employing the $\text{DFT}+\text{DMFT}$ method. Our results clarify the $B\text{1-type}$ CeN is in a mixed-valence state at ambient pressure. However, as the system experiences compression and tension, CeN undergoes multiple quantum phase transitions, transitioning from a mixed-valence state to a Kondo metal and ultimately to an insulator. Importantly, it is observed that the number of occupied $4f$ electrons $n_f$ of Ce increases as the temperature and pressure increase within the mixed-valence regime, contrasting with the behavior observed in the Kondo regime, the $n_f$ is very stable, nearly one. Furthermore, we also investigate the high-pressure phase of $B2\text{−}\mathrm{type}$ CeN, it also presents mixed-valence and Kondo metal phases transition by tuning stress. Our paper illustrates stress as a clean method to tune quantum phase transitions in CeN by changing the states of $f$ electrons and clarifying the physical driving force of phase transitions.