Beyond a cluster-Mott state in the breathing kagome lattice of LiZn2Mo3O8

Searching of materials, where a long-range magnetic order is suppressed by quantum fluctuations and a quantum spin liquid state realizes, is one of the central problems in the modern condensed matter physics. A possible candidate for such a state on the breathing Kagome lattice LiZn2Mo3O8 is scrutinized by hard x-ray photoemission spectroscopy (HAXPES), cluster dynamical mean-field theory (cDMFT), and exact diagonalization of an extended Hubbard model. The Mo 3d core level HAXPES peaks of LiZn2Mo3O8 are accompanied by shoulders on their lower energy side which are absent in Zn2Mo3O8. The shoulder peaks observed only in LiZn2Mo3O8 indicate Mo3+ and Mo4+ charge fluctuations. The cDMFT calculations not only describe experimental valence-band HAXPES spectra demonstrating importance of the correlation effects, but also feature nonlocal spin fluctuations. Exact diagonalization taking into account intertrimer Coulomb repulsion demonstrates long-range charge fluctuations consistent with HAXPES results.