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Séminaire MCBT

Mardi 13 mai 2014 à 11h00,
Salle Louis weil, E424,

Orateur : Karim Ferhat (Institut Néel, CNRS)
"Phase diagram of the 1/3 filled extended Hubbard model on the Kagome lattice"

Strongly correlated systems on frustrated lattices can exhibit very interesting physics ranging from spin liquids, valence bond physics, fractionalized defects, and unconventional electronic phases (pinballs, pined metal droplets). In that respect, Kagome lattices are the most geometrically frustrated systems in two dimensions and are at the center of intense research activity these last years.

In this work, we have studied the phase diagram of an extended Hubbard model on the kagome lattice at 1/3 filling at which the system is known to exhibit a classically degenerate ground state manifold characterized by a local "ice-rule" constraint (the system is enforced to fulfills peculiar conditions on each triangle of the lattice). This degeneracy can be lifted up by quantum fluctuations and exotic phases are expected to be stabilized. In this presentation, we discuss the rich phase diagram obtained in this system by combining a configuration interaction approach to an unrestricted Hartree-Fock, in order to partially bring back the correlations lost in the mean-field solution.

In particular, we present two original phases, one consisting of an enlarged polarized kagome charge order (pins), with relatively high kinetic energy coming from 6-site metallic chains inversely polarized on hexagons (droplets). In this phase, the energy is also decreased thanks to spin-resonating processes between the droplets, and the pins. The second is driven by an antiferromagnetically coupling of spins and is constituted of disconnected 6-spin singlet rings. Interestingly enough, this phase is stabilized by effective Heisenberg interactions emerging via both charge and spin degrees of freedom. Finally, we provide a complete description of these phases and their mechanisms by using a trial wave function in the very strong interaction limit which reproduces very precisely their ground state properties.

[1] Phys. Rev. B 89, 155141

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