Trimer Formation and Metal-Insulator Transition in Orbital Degenerate Systems on a Triangular Lattice

Abstract

As a prototypical self-organization in the system with orbital degeneracy, we theoretically investigate trimer formation on a triangular lattice, as observed in LiVO2. From the analysis of an effective spin-orbital coupled model in the strong correlation limit, we show that the previously-proposed orbital-ordered trimer state is not the lowest-energy state for a finite Hund's-rule coupling. Instead, exploring the ground state in a wide range of parameters for a multiorbital Hubbard model, we find an instability toward a different orbital-ordered trimer state in the intermediately correlated regime in the presence of trigonal crystal field. The trimer phase appears in the competing region among a paramagnetic metal, band insulator, and Mott insulator. The underlying mechanism is nesting instability of the Fermi surface by a synergetic effect of Coulomb interactions and trigonal-field splitting. The results are compared with experiments in triangularlattice compounds, LiVX2 (X=O, S, Se) and NaVO2.

4 pages, 4 figures, accepted for publication in J. Phys. Soc. Jpn

References in corpus (5)

• Anomalous metallic state in the vicinity of Metal to Valence Bond Solid insulator transition in LiVS2
• The crucial importance of the $t_{2g}$--$e_g$ hybridization in transition metal oxides
• Role of Orbitals in the Physics of Correlated Electron Systems
• Orbitally relieved magnetic frustration in NaVO2
• Spin Singlet State in Heptamers Emerging in Spinel Oxide AlV${}_2$O${}_4$

Cited by in corpus (6)

• Hubbard-corrected DFT energy functionals: the LDA+U description of correlated systems
• Regular-Triangle Trimer and Charge Order Preserving the Anderson Condition in the Pyrochlore Structure of CsW${}_2$O${}_6$
• Vanadium trimers randomly aligned along the c-axis direction in layered LiVO2
• Orbital reformation with vanadium trimerization in $d^2$ triangular lattice LiVO${}_2$ revealed by ${}^{51}$V NMR
• Mott-to-Goodenough insulator-insulator transition in LiVO${}_2$
• Hidden spin-orbital hexagonal ordering induced by strong correlations in LiVS${}_2$