Emergent orbitals in the cluster Mott insulator on a breathing Kagome lattice

Abstract

Motivated by the recent developments on cluster Mott insulating materials such as the cluster magnet LiZn${}_2$Mo${}_3$O${}_8$, we consider the strong plaquette charge ordered regime of the extended Hubbard model on a breathing Kagome lattice and reveal the properties of the cluster Mottness. The plaquette charge order arises from the inter-site charge interaction and the collective motion of three localized electrons on the hexagon plaquettes. This model leads naturally to a reduction of the local moments by 2/3 as observed in LiZn${}_2$Mo${}_3$O${}_8$. Furthermore, at low temperatures each hexagon plaquette contains an extra orbital-like degree of freedom in addition to the remaining spin 1/2. We explore the consequence of this emergent orbital degree of freedom. We point out the interaction between the local moments is naturally described by a Kugel-Khomskii spin-orbital model. We develop a parton approach and suggest a spin liquid ground state with spinon Fermi surfaces for this model. We further predict an emergent orbital order when the system is under a strong magnetic field. Various experimental consequences for LiZn${}_2$Mo${}_3$O${}_8$ are discussed, including an argument that the charge ordering much be short ranged if the charge per Mo is slightly off stoichiometry.

arXiv comment12 pages, 13 figures

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• Multiflavor Mott insulators in quantum materials and ultracold atoms
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• Quantum spin liquid and cluster Mott insulator phases in the Mo${}_3$O${}_8$ magnets
• LiZn${}_2$V${}_3$O${}_8$: A new geometrically frustrated cluster spin-glass
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• Extended Coulomb liquid of paired hardcore boson model on a pyrochlore lattice
• Theory of partial quantum disorder in the stuffed honeycomb Heisenberg antiferromagnet
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• Classical phase diagram of the stuffed honeycomb lattice
• Multipeak quasielastic light scattering and high-frequency electronic excitations in honeycomb Li${}_2$RuO${}_3$
• Is spontaneous vortex generation in superconducting 4Hb-TaS${}_2$ from vison-vortex nucleation with ${\mathbb{Z}}_2$ topological order?
• Inelastic light scattering in the spin cluster Mott insulator Cu${}_2$OSeO${}_3$
• Coupled dynamics of long-range and internal spin cluster order in Cu${}_2$OSeO${}_3$
• Antiferromagnetic Spin Fluctuations and Structural Transition in Cluster Mott Insulator Candidate Nb3Cl8 Revealed by 93Nb- and 35Cl-NMR
• Kinetic Energy Driven Ferromagnetic Insulator