Charge fluctuations in a cluster Mott state: Hard x-ray photoemission study on a breathing kagome magnet Nb3Cl8

We report on our hard x-ray photoemission study of Nb₃Cl₈, wherein the breathing Kagome lattice of Nb provides interesting magnetic properties with spin 1/2 per Nb trimer. The Nb0.16em0ex3d5/2 and 3d3/2 core level peaks are accompanied by satellite peaks, suggesting the importance of Nb0.16em0ex4d charge degrees of freedom. The Cl0.16em0ex1s and $2p$ core level spectra have high binding energy peaks which can be assigned to the Cl site with Cl0.16em0ex3p ligand holes near the center of the Nb trimer. The core level spectra indicate that the Nb-Nb and Nb-Cl charge fluctuations play crucial roles in the magnetic interaction between the trimers.