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.

12 pages, 13 figures

References in corpus (6)

• U(1) Gauge Theory of the Hubbard Model : Spin Liquid States and Possible Application to k-(BEDT-TTF)_2 Cu_2 (CN)_3
• Valence Bond Solids and Their Quantum Melting in Hard-Core Bosons on the Kagome Lattice
• Possible valence-bond condensation in the frustrated cluster magnet LiZn2Mo3O8
• Kinetic ferromagnetism on a kagome lattice
• Coulomb liquid phases of bosonic cluster Mott insulators on a pyrochlore lattice
• Electronic tunability of the frustrated triangular-lattice cluster magnet LiZn${}_{2-x}$Mo${}_3$O${}_8$

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• Is spontaneous vortex generation in superconducting 4Hb-TaS${}_2$ from vison-vortex nucleation with ${\mathbb{Z}}_2$ topological order?
• Antiferromagnetic Spin Fluctuations and Structural Transition in Cluster Mott Insulator Candidate Nb3Cl8 Revealed by 93Nb- and 35Cl-NMR
• Kinetic Energy Driven Ferromagnetic Insulator