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TT: Tiefe Temperaturen

TT 6: Correlated Electrons - (General) Theory I

TT 6.3: Vortrag

Freitag, 4. März 2005, 14:30–14:45, TU H2053

Phase diagram of the half-filled two-dimensional SU(N) Hubbard-Heisenberg model. — •Fakher Assaad — Universität Würzburg

We investigate the phase diagram of the half-filled SU(N) Hubbard-Heisenberg model with hopping t, exchange J and Hubbard U, on a two-dimensional square lattice. In the large-N limit, and as a function of decreasing values of t/J, the model shows a transition from a d-density wave state to a spin dimerized insulator. A similar behavior is observed at N=6 whereas at N=2 a spin density wave insulating ground state is stabilized. The N=4 model, has a d-density wave ground state at large values of t/J which as a function of decreasing values of t/J becomes unstable to an insulating state with no apparent lattice and spin broken symmetries. In this state, the staggered spin-spin correlations decay as a power-law, resulting in gapless spin excitations at q^→ = (π,π). Furthermore, low lying spin modes with small spectral weight are apparent around the wave vectors q^→ = (0,π) and q^→ = (π,0). This gapless spin liquid state is equally found in the SU(4) Heisenberg ( U/t → ∞ ) model in the self-adjoint antisymmetric representation. An interpretation of this state in terms of a π-flux phase is offered. Our results stem from projective (T=0) quantum Monte-Carlo simulations on lattice sizes ranging up to 24 × 24.