• Exact ground states;
  • non-integrable organic hexagon chains;
  • ferromagnetism;
  • polyphenylene.


A technique based on positive semidefinite operator properties has been used in deducing exact ground states for hexagon chains of polyphenylene type (hexagons interconnected by bonds build up the 1D periodic structure), placed in a constant external magnetic field B perpendicular to the surface containing the system. The used Hubbard type of model takes into account B by Peierls phase factors, and has the peculiar property to provide only flat bands in the bare band structure for elevated external field values independent on the parameters entering in the kinetic part of the Hamiltonian. The deduced ground states are non-magnetic or ferromagnetic in character, localized in the thermodynamic limit, and besides the fact that B is able to switch the system between different phases, emphasize that the localization length and connectivity conditions can be tuned by external magnetic fields.