Haldane insulator protected by reflection symmetry in the doped Hubbard   model on the three-legged ladder
  We demonstrate the existence of an insulating phase in the three-legged Hubbard ladder at two-thirds filling. In this phase chargons are bound because the physics within a unit cell favors the formation of triplets. The resultant moments lead to a ground state in the Haldane phase, a symmetry protected topological state of matter. In this purely fermionic model, reflection is protecting but time reversal and dihedral symmetries are not, in contrast to spin models. 
H. L. Nourse, I. P. McCulloch, C. Janani, and B. J. Powell
cond-mat.str-el