Coherent and Ultracoherent States in Hubbard and Related Models
We consider the Hubbard model and extensions on bipartite lattices. We define a dynamical group based on the η-pairing operators introduced by Yang, and define coherent pairing states, which are combinations of eigenfunctions of η operators. The coherent states are defined through the exponentiation of η-operators. In addition we introduce the so-called ultracoherent states through exponentiation of certain functions of η-operators. The coherent states permit exact calculation of numerous physical properties of the system, including energy, various fluctuation and correlation functions, as well as pairing off-diagonal long-range order (ODLRO) to all orders. This approach is complementary to that of BCS, in that these are superconducting coherent states associated with the exact model, while not eigenstates of the Hamiltonian.
KeywordsCoherent State Hubbard Model Spin Coherent State Variational Wave Function True Ground State
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