Fermi surface of LaRu 4 P 12 : A clue to the origin of the metal-insulator transition in PrRu 4 P 12

We report the de Haas\char21{}van Alphen (dHvA) effect and magnetoresistance in the filled-skutterudite superconductor ${\mathrm{LaRu}}_{4}{\mathrm{P}}_{12}$, which is a reference material of ${\mathrm{PrRu}}_{4}{\mathrm{P}}_{12}$ that exhibits a metal-insulator (M-I) transition at ${T}_{\mathrm{MI}}\ensuremath{\simeq}60\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The observed dHvA branches for the main Fermi surface (FS) are well explained by the band-structure calculation, using the full potential linearized augmented-plane-wave method with the local-density approximation, suggesting a nesting instability with $\mathbf{q}=(1,0,0)$ in the main multiply connected FS as expected also in ${\mathrm{PrRu}}_{4}{\mathrm{P}}_{12}$. Observed cyclotron effective masses of $(2.6\ensuremath{-}11.8){m}_{0}$, which are roughly twice the calculated masses, indicate the large mass enhancement even in the La-skutterudites. Comparing the FS between ${\mathrm{LaRu}}_{4}{\mathrm{P}}_{12}$ and ${\mathrm{PrRu}}_{4}{\mathrm{P}}_{12}$, an essential role of $c\text{\ensuremath{-}}f$ hybridization cooperating with the FS nesting in driving the M-I transition in ${\mathrm{PrRu}}_{4}{\mathrm{P}}_{12}$ is clarified.