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Séminaire MCBT

mardi 6 octobre 2015 à 11h00,
Salle Louis Weil, E424

Orateur : Clément Février (Institut NEEL - TMC)
"Multi-orbital kinetic effects on electrons in triangular lattice"

Abstract :

Strongly correlated electron systems are often characterized by complex phase diagrams, reflecting an intricate interplay between magnetic, charge and orbital degrees of freedom. The role of the multiorbital effects on the emergence of electronic orders on the frustrated triangular lattice at half-filling is investigated though a spinless extended Hubbard model. The latter is expected to describe layered triangular compounds, such as AgNiO2 which exhibits a threefold charge order[1], or transition metal dichalcogenides where a variety of charge ordered phases have been observed[2].
Using complementary approaches, exact diagonalizations and unrestricted Hartree-Fock calculations, we unravel a very rich phase diagram with a competition between homogeneous, charge ordered and orbitally ordered phases, controlled by the strength of both local and short-range Coulomb interactions and by the hopping integrals of eg orbitals.
Among the unconventional electronic states, we will focus this presentation on the charge ordered phases. We find in particular, an original pinball liquid, which is a metallic charge ordered state where localized (pins) and itinerant electrons (balls) coexist, that was first devised in the context of quarter-filled organic conductors[3]. By changing the anisotropic ratio t’/t of the hopping integrals, an inverse pinball liquid occurs, where the role of charge-rich and charge-poor sites are interchanged, an insulating large unit cell √12 × √12 droplet phase can be stabilized[4], with a periodicity close to the √13 × √13 David Star charge order presents in 1T-TaS2.
These electronic states are generic for the half-filled triangular lattice and are also found in the isotropic limit, which corresponds to the single-band spinful extended Hubbard model.

[1] G. L. Pascut, et al., Phys. Rev. Lett., 106, 157206 (2011).
[2] B. Sipos, et al., Nat. Mater. 7, 960 (2008).
[3] L. Cano-Cortés, A. Ralko, C. Février, J. Merino, and S. Fratini, Phys. Rev. B, 84, 155115 (2011).
[4] C. Février, S. Fratini, A. Ralko, Phys. Rev. B, 91, 245111 (2015).

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