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 $T_{CDW}\sim 160$ 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 $\sim 2$ 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 ${\mathrm{Ce}}_3{\mathrm{Co}}_4{\mathrm{Sn}}_{13}$.

• Received 25 June 2018
• Revised 21 November 2018

DOI:https://doi.org/10.1103/PhysRevB.98.235136