Hard x-ray photoelectron spectroscopy of the metal-insulator transition in LiRh2O4

We have applied hard x-ray photoelectron spectroscopy to LiRh${}_{2}$O${}_{4}$ to study its bulk electronic structures. LiRh${}_{2}$O${}_{4}$ shows the metal-insulator transition (MIT) at 170 K when the temperature is decreased via an intermediate phase, which appears below 230 K and is ascribed to the band Jahn-Teller instability. Clear spectral changes are observed across the MIT for both the valence band near the Fermi level (${E}_{F}$) and the Rh 3$d$ core state. Their slight spectral changes are also observed across 230 K, induced by the orbital ordering and the slight change of the screening by conduction electrons. The linear polarization dependence of the spectra was measured for the O 2$s$ and valence-band states. The contribution of the Rh 5$s$ state hybridized with the O 2$p$ states in the valence band is semiquantitatively evaluated.