The SLAC real-space renormalization group method is used to study one-dimensional antiferromagnetic chains at zero temperature. Calculations using three-site blocks (for the Heisenberg-Ising model) and two-site blocks (for the isotropic Heisenberg model) are compared with exact results. In connection with the two-site calculation a duality transformation is introduced under which the isotropic ...

The Higgs mode is expected to exist in any system with the spontaneous symmetry breaking of the continuous symmetry. We make numerical study about the Higgs mode in the Heisenberg antiferromagnet on the square lattice by the exact diagonalisation approach. Since the Higgs mode can couple with a pair of the Nambu-Goldstone modes, we calculate the dynamical correlation of the two spin operators, ...

The magnetic excitations of the double-exchange (DE) model are usually discussed in terms of an equivalent ferromagnetic Heisenberg model. However this equivalence is valid only at a quasi-classical level—we show that both quantum and thermal corrections to the magnetic properties of the DE model differ from any effective Heisenberg model because its spin excitations interact only indirectly, t...

ABSTRACT: We investigate the mechanism of spin gap formation in a two-dimensional model relevant to Mott insulators such as CaV4O9. From the perturbation expansion and quantum Monte Carlo calculations, the origin of the spin gap is ascribed to the four-site plaquette singlet in contrast to the dimer gap established in the generalized dimerized Heisenberg model. We investigate the mechanism of s...

in the Spin-2 J1-J2 Square Heisenberg Model Shou-Shu Gong, Wei Zhu, D. N. Sheng, Olexei I. Motrunich, and Matthew P. A. Fisher Department of Physics and Astronomy, California State University, Northridge, California 91330, USA Department of Physics, California Institute of Technology, Pasadena, California 91125, USA Department of Physics, University of California, Santa Barbara, California 9310...

We have studied the Heisenberg model on the triangular lattice using quantum Monte Carlo techniques (up to 144 sites) and exact diagonalization (up to 36 sites). By studying the spin gap as a function of the system size we have obtained robust evidence for a gapless spectrum, confirming the existence of long-range Néel order. Our best estimate is that in the thermodynamic limit the order parame...

Custodial SU(2) breaking due to dynamical fermion masses is studied in a rather general context and it is shown how some well known limiting cases are correctly described. The type of “gap equation” which can systematically lead to extra negative contributions to the so–called ρ–parameter is emphasized. Furthermore general model independent features are discussed and it is shown how electro–wea...

A new 2-parameter quadratic deformation of the quantum oscillator algebra and its 1-parameter deformed Heisenberg subalgebra are considered. An infinite dimensional Fock module representation is presented which at roots of unity contains null vectors and so is reducible to a finite dimensional representation. The cyclic, nilpotent and unitary representations are discussed. Witten’s deformation ...