Correlated flat bands and quantum spin liquid state in a cluster Mott insulator
Jiayu Hu, Xuefeng Zhang, Cong Hu, Jian Sun, Xiaoqun Wang, Hai‐Qing Lin, Gang Li
Abstract
Abstract Flat bands are rare in pristine solids and are unstable against electronic correlations or other types of long-range order. Unlike atomic-scale Hubbard systems or Moiré materials, where electronic correlations are either localized or long-ranged, pristine flat band systems with short-range interactions that do not break symmetry spontaneously are less known and intriguing. These systems could bridge the gap between atomic Mott insulators and Moiré correlated insulators, offering a unique platform to explore their mysterious relation. Using an analytical analysis, further verified by numerical calculations, we show that monolayer Nb 3 Cl 8 is a unique flat band system with short-range interactions. We present clear evidence that it is a cluster Mott insulator, which nicely explains the electronic structure observed in angle-resolved photoemission spectroscopy. We further propose that monolayer Nb 3 Cl 8 may constitute a rare example of molecular quantum spin liquid with flat bands.