Nagaoka physics in kinetically frustrated electronic models.

C. GAZZA

Natal

Simposio; Workshop and Symposium on DMRG Technique for Strongly Correlated Systems in Physics and Chemistry; 2015

nternational Institute of Physics. Universidade Federal do Rio Grande do Norte

The Nagaoka's theorem is one of the few exact results about itinerant magnetism. In certain electronic systems, the kinetic energy is frustrated due to quantum interference hopping processes, and this frustration phenomenon invalidates the Nagaoka's theorem. In this work we study the magnetic properties of a strongly correlated electron model, in which the existence of kinetic frustration is governed by the sign of the hopping integral t. In particular, we compute the ground state of the infinite U Hubbard model on the triangular lattice with a positive t, and on the square lattice with positive second-neighbor hopping term t2=t1, by means of the density matrix renormalization group technique. We find that, for one hole doped away from half-filling, both models have an antiferromagnetic ground state: a 120° Neel order on the triangular lattice, and the usual Neel order in the square case. Notably, in these extremely correlated quantum models, spin fluctuations die off and the local magnetization takes the classical value. We identify the mechanism of this kinetic antiferromagnetism with the release of the kinetic energy frustration as the hole moves in the established antiferromagnetic background. This release can occurs in two different ways: by a non-trivial spin-Berry phase acquired by the hole or by the effective vanishing of the hopping amplitude along the frustrating loops. We also discuss the fate of the ferromagnetic Nagaoka ground state considering anisotropic hopping terms t' on the triangular lattice. An important result is the classical character of the magnetic order for all the values of t' studied.