Dresden 2003 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 2: Systeme korrelierter Elektronen I
TT 2.3: Vortrag
Montag, 24. März 2003, 10:30–10:45, HSZ304
Ground-state phase diagram of the half-filled one-dimensional extended Hubbard model — •Eric Jeckelmann — Philipps-Universität, FB Physik, 35032 Marburg
The density-matrix renormalization-group method is used to study the ground-state phase diagram of the one-dimensional half-filled Hubbard model with on-site (U) and nearest-neighbor (V) repulsion, and hopping term t. It is shown that only a critical line Vc(U) ≈ U/2 separates a Mott insulating phase [V < Vc(U)] from a long-range ordered charge-density-wave phase [V > Vc(U)]. At a tricritical point (Ut≈ 3.7, Vt=2t) the quantum phase transition changes from continuous for weak coupling to first order for strong coupling. The competition between free and bound charge excitations in the low-energy spectrum is responsible for the change of the transition order. The tricritical point position is determined by the intersection of the critical line Vc(U) with the boundary V=2t between free and bound charge excitations in the Mott insulating phase. On the critical line Vc(U), a frustrating effective antiferromagnetic coupling of the spin degrees of freedom gives rise to a long-range ordered bond-order-wave phase at intermediate U starting from the tricritical point (Ut < U < ≈ 7t). [E. Jeckelmann, Phys. Rev. Lett. 89, 236401 (2002).]