YCl Electride as a Multi-Orbital Correlated Topological Dice Lattice System

Abstract

The long-sought dice lattice flat band has recently been discovered for the first time in two-dimensional layered electride yttrium monochloride (YCl) [Nature Communications 17, 2213 (2026)]. While essential flat band features of YCl were captured by an idealized simple dice lattice model, we reveal in this Letter that a unique layer-orbital-valley coupling in YCl puts up a fundamental obstruction against a simple three-band dice lattice description of the flat band, and necessitates a multi-orbital description that faithfully represents the symmetry, topology, and correlation physics in the first-ever dice metal. Using an ab initio based multi-orbital Hubbard model with local interactions, we predict that the multi-orbital flat band supports a robust ferromagnetic ground state and electrically tunable correlated quantum anomalous Hall phases that are absent in an interacting single-orbital dice lattice. Our findings open a new avenue for exploring correlation and topology in electride systems.