Emergence of topological defects and spin liquid in a two-orbital spin-fermion model on the honeycomb lattice

Stabilizing exotic quantum phases of matter, e.g., spin liquid, is an attractive topic in condensed matter. Here, by a Monte Carlo study of a two-orbital spin-fermion model on a honeycomb lattice, we show that the cooperative effects of the orbital degeneracy of itinerant electrons and the exchange interaction of localized spins can significantly suppress both ferromagnetic and antiferromagnetic orders by generating topological defects, and give rise to an intermediate spin-liquid state via continuous phase transitions. This phase competition can also be achieved by tuning the electron filling. These results shed light on realizing spin liquids on geometrically nonfrustrated lattices.