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...

We show that the algebra of commuting Hamiltonians of the homogeneous XXX Heisenberg model has simple spectrum on the subspace of singular vectors of the tensor product of two-dimensional gl 2 -modules. As a byproduct we show that there exist exactly ( n l )

In this problem you will consider the Heisenberg model of a one-dimensional quantum antiferromagnet. I first give you a brief summary on the Heisenberg model. You do not need to have any previous knowledge on magnetism (or the Heisenberg model) to do this problem. You will be able to solve this problem only with the methods that were discussed in class. The one-dimensional Heisenberg model is d...

In this paper the the effect of Dzyaloshinskii-Moriya interaction and anisotropy on the Entanglement of Heisenberg chain has been studied. While the anisotropy suppress the entanglement due to favoring of the alignment of spins, the DM interaction restores the spoiled entanglement via creation of the quantum fluctuations. Thermodynamic limit of the model and emerging of nonanalytic behavior of ...

The ground-state properties of the square-lattice spin-1/2 Heisenberg antiferromagnet with spatially anisotropic couplings are investigated by Green’s-function projection approaches. The staggered magnetization and the two-spin correlators are calculated; the competition between magnetic longand short-range order is discussed in comparison with experiments on Sr2[Ca2]CuO3.

In the recent article Phys. Lett. B 2016, 759, 424–429, a new class of field theories called Nonlinear Field Space Theory was proposed. In this approach, the standard field theories are considered as linear approximations to some more general theories characterized by nonlinear field phase spaces. The case of spherical geometry is especially interesting due to its relation with the spin physics...