New symmetry properties of a class of Hubbard models

Harald Grosse

H. Q. Lin, David K Campbell, Rudolf Torsten Clay

Wepresent analytical and numerical studieson thephasediagramof theone-dimensional extended Hubbard model. PACS. 75.10.–b – General theory and models of magnetic ordering. PACS. 75.10.Jm – Quantized spin models. Thepast two decades havewitnessed thediscoveries of several new classes of novel elec-tronic materials. Ranging fromconducting polymers through chargetransfer solids and inorganic chain compounds to organic and high temperaturesuperconductors, thesematerials have in com-mon two important, unusual properties. First, their electronic structures are strongly anisotropic,

Z. Maassarani

A class of recently introduced su (n) "free-fermion" models has recently been used to construct generalized Hubbard models. I derive an algebra defining the "free-fermion" models and give new classes of solutions. I then introduce a conjugation matrix and give a new and simple proof of the corresponding decorated Yang–Baxter equation. This provides the algebraic tools required to couple in an integrable way two copies of free-fermion models. Complete integrability of the resulting Hubbard-like models is shown by exhibiting their L and R matrices. Local symmetries of the models are discussed. The diagonalization of the free-fermion models is carried out using the algebraic Bethe Ansatz.

E. Ahmed, A. S. Hegazi

James C. Osborn

The meron-cluster algorithm was previously used to extensively study the physics associated with the spontaneous breaking of a discrete symmetry. We recently discovered that a larger class of models with spontaneous breaking of continuous symmetries can also be simulated using the meron-cluster algorithm. Here we study one of these new models which belongs to the attractive Hubbard model family. In particular we study the spontaneous breaking of the U(1) fermion number symmetry in two dimensions and find clear evidence for a Kosterlitz-Thouless transition to a superconducting phase. 1.

E. Ahmed, Ahmed Sadek Hegazi