Stanford University

The layered sodium cobaltate, Na_xCoO₂, has attracted substantial attention because of its abnormally large Seebeck coefficient and the emergence of superconductivity when intercalated with water. These exotic electronic properties are generally attributed to electron correlation, but have not been fully understood. Therefore, it is interesting to study an isostructural material, K_xRhO₂, in which the strongly correlated 3d electrons are replaced by their 4d siblings. In this work, we employ angle-resolved photoemission spectroscopy (ARPES) to measure the electronic structure of K_xRhO₂ for different K concentrations (0.39 ≤ x ≤ 0.62). We find that the bandwidth is renormalized by a factor of 1.1-1.3, suggesting a significant reduction of correlation when comparing to Na_xCoO₂. The measured Fermi surface consists of only one hole pocket around the zone center, while the small pockets near zone corner predicted by calculation are found to sink below the Fermi energy. We also discover a kink in the low energy quasiparticle dispersion, which could be explained by a coupling between electrons and phonons.