Electronic structure investigation of a charge density wave coupled to a metal-to-metal transition in Ce3Co4Sn13

Abstract

We study the electronic structure of the skutterudite ${\mathrm{Ce}}_{3}{\mathrm{Co}}_{4}{\mathrm{Sn}}_{13}$, which is known to exhibit a charge density wave (CDW) transition, at temperature ${T}_{CDW}\ensuremath{\sim}160$ K, coupled to a metal-to-metal transition. We use temperature dependent hard x-ray photoemission spectroscopy (HAXPES) and x-ray absorption spectroscopy (XAS) to investigate the occupied and unoccupied electronic states of ${\mathrm{Ce}}_{3}{\mathrm{Co}}_{4}{\mathrm{Sn}}_{13}$. The Co $2p$ and Sn $3p$ core level spectra show small but finite shifts in binding energy positions across ${T}_{CDW}$ while Ce $3d$ core level spectra do not show any change across the transition. The Ce ${M}_{4,5}$-edge XAS spectrum compared with calculations indicate a typical trivalent ionic ${\mathrm{Ce}}^{3+}$ spectral shape, ruling out Kondo screening in ${\mathrm{Ce}}_{3}{\mathrm{Co}}_{4}{\mathrm{Sn}}_{13}$. In contrast, the Co ${L}_{2,3}$-edge XAS spectrum compared with a calculated spectrum shows evidence for hybridization with neighboring Sn atoms in a trigonal prismatic co-ordination. Temperature dependent XAS across the Co ${L}_{2,3}$-edge shows a small shift across ${T}_{CDW}$, consistent with HAXPES results. Detailed XAS measurements as a function of temperature show that the spectral shifts occur with a hysteresis across ${T}_{CDW}$, indicative of a first-order transition. Valence band spectra show a normal Fermi edge above and below ${T}_{CDW}$. The Co $3d$ states are observed at a binding energy of $\ensuremath{\sim}2$ eV while the Ce $4f$ states occur as a weak feature within 0.5 eV of the Fermi level. The results suggest an unusual CDW transition coupled to a metal-to-metal transition in ${\mathrm{Ce}}_{3}{\mathrm{Co}}_{4}{\mathrm{Sn}}_{13}$.