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Abstract
From known phase diagram regions of different model Hamiltonians describing strongly correlated systems we deduced new domains of the ground state phase diagram of the same models by a unitary transformation. Different types of extended Hubbard Hamiltonians were used for the starting point and the existence of new stable spin-density waves, charge-density waves, ferromagnetic states and a paramagnetic insulator is demonstrated. The procedure used is dimension independent. The ground state phase diagrams of several strongly correlated systems modelled by extended Hubbard-like Hamiltonians are analysed using unitary transformations. New stable spin-density wave, charge-density wave, ferromagnetic or paramagnetic insulator phases are obtained in different cases. The results are true in any dimensions.
SUMMARY
In this paper, we have presented a procedure based on an explicitly given unitary transformation which allows the rigorous deduction of new phase diagram domains starting from known ground state solutions of a given model. The method is not model dependent and can be applied for arbitrary dimensions. We have applied this method to find new stable spin-density wave, charge-density wave, ferromagnetic and paramagnetic insulator domains of different extended Hubbard type models.