Emergence of diverse lanthanum fluorides under high pressure: From insulators to half-metals and superconductors

We present a comprehensive first-principles investigation of the La-F system in rare-earth fluorides under pressures ranging from 50 to 300 GPa. Our study reveals the existence of novel F-rich phases $\mathrm{La}{\mathrm{F}}_{5}$ and $\mathrm{La}{\mathrm{F}}_{6}$ with $F\text{\ensuremath{-}}43m$ and $R3$ symmetry, respectively, in addition to the known insulating $\mathrm{La}{\mathrm{F}}_{3}$. $\mathrm{La}{\mathrm{F}}_{5}$, a binary derivative of half-Heusler alloys, exhibits half-metallic ferromagnetism between 14 and 100 GPa, with large band gaps of 5.7--6.9 eV of the spin-up channel and high Curie temperatures of 673--505 K. Electronic analysis attributes the ferromagnetic and half-metallic properties to F atoms in tetrahedral motifs. Furthermore, we predict that trigonal $\mathrm{La}{\mathrm{F}}_{6}$, characterized by layered stacking structures, exhibits superconductivity with a critical temperature $({T}_{\mathrm{c}})$ of 5 K at 50 GPa. Our findings provide valuable insights into the high-pressure behavior of rare-earth fluorides and their potential applications in advanced materials and devices.