Showing papers by "Eugene J. Mele published in 1991"

Phase diagram of the one-dimensional t-J model from variational theory.

Abstract: We study a class of variational wave functions for strongly interacting one-dimensional lattice fermions in which correlations among the particles are specified by a single variational parameter. We find that the wave functions describe the ground-state properties of the one-dimensional t-J model remarkably well over the entire phase diagram in which interaction strength and density are varied. Specifically the wave function describes a Tomonaga-Luttinger liquid at low J/t, a phase-separated state at large J/t, and a stable state with infinite compressibility between these phases at low densities.

Local canonical transformations of fermions

Abstract: By permitting canonical transformations that are nonlinear in fermion creation and annihilation operators, we show that the space of canonical transformations of ordinary spin-1/2 operators local to a point in space is SU(2)\ensuremath{\bigotimes}SU(2)\ensuremath{\bigotimes}U(1)\ensuremath{\bigotimes}${\mathit{Z}}_{2}$. We identify those subgroups that form local and global gauge symmetries of the Hubbard-Heisenberg model on and off half filling. Our systematic method of generating all ocal canonical transformations enables us to discover a ``nonlinear'' local U(1) gauge symmetry of the Heisenberg-Hubbard model that remains a local symmetry away from half filling. The paper presents this group together with all other known canonical transformations in a unified framework.

Variational Many Body States for the U=∞ Hubbard Model

Abstract: We study a general class of variational wavefunctions for strongly correlated lattice fermions. The wavefunctions considered here automatically satisfy local constraints of no double occupancy and include correlations between opposite spin particles in a very physical way. We calculate the energy and correlation functions for the one dimensional U=∞ Hubbard model, where a comparison with exact results is made. We briefly report on preliminary results for the t-J model.

Statistical transmutation in diluted flux states

Abstract: We investigate a generalization of the commensurate-flux-state theory of the diluted t-J model in which fluctuations in the self-induced gauge field are coupled to the hole coordinates. Doped fermionic holes in the theory carry an internal SU(2)\ifmmode\times\else\texttimes\fi{}SU(2) degree of freedom, and a polarization of this internal field leads to fractionization of the quantum statistics of the particles. The many-semion states of the model are studied by an application of the Atiyah-Singer index theorem to investigate the dynamics of these diluted flux states.