60 research outputs found
Spatially anisotropic Heisenberg Kagome antiferromagnet
In the search for spin-1/2 kagome antiferromagnets, the mineral volborthite
has recently been the subject of experimental studies [Hiroi et al.,2001]. It
has been suggested that the magnetic properties of this material are described
by a spin-1/2 Heisenberg model on the kagome lattice with spatially anisotropic
exchange couplings. We report on investigations of the Sp(N) symmetric
generalisation of this model in the large N limit. We obtain a detailed
description of the dependence of possible ground states on the anisotropy and
on the spin length S. A fairly rich phase diagram with a ferrimagnetic phase,
incommensurate phases with and without long range order and a decoupled chain
phase emerges.Comment: 6 pages, 6 figures, proceedings of the HFM2006 conference, to appear
in a special issue of J. Phys.: Condens. Matte
The Influence of Distributed Leadership on Effective School Governance and Improved School Performance A Study Conducted in Two Private Schools in the UAE
The purpose of this research is to identify the impact of Distributed Leadership (DL) on school governance, leading to an improvement in the overall school performance. This study was conducted in two private schools in the UAE. The review of related literature helped to understand the concept of distributed leadership and its impact on governance, school performance, and organizational hierarchy. The data was collected using a mixed method using surveys and interviews. The data was analyzed using descriptive analysis and moderated regression analysis. The conclusion reached was that DL has a positive impact on the relationship between governance and performance. It was also found that DL was being applied in both schools at varying levels, and each had areas that needed improvement. The most important implication was the connection of DL to governance and performance. The findings offer relevant insights for schools studied, as well as for similar schools
Topological Confinement and Superconductivity
We derive a Kondo Lattice model with a correlated conduction band from a
two-band Hubbard Hamiltonian. This mapping allows us to describe the emergence
of a robust pairing mechanism in a model that only contains repulsive
interactions. The mechanism is due to topological confinement and results from
the interplay between antiferromagnetism and delocalization. By using
Density-Matrix-Renormalization-Group (DMRG), we demonstrate that this mechanism
leads to dominant superconducting correlations in a 1D-system.Comment: 4 pages, 4 figure
Effective Low-Energy Model for f-Electron Delocalization
We consider a Periodic Anderson Model (PAM) with a momentum-dependent
inter-band hybridization that is strongly suppressed near the Fermi level.
Under these conditions, we reduce the PAM to an effective low-energy
Hamiltonian, , by expanding in the small parameter (
is the maximum inter-band hybridization amplitude and is the hopping
integral of the broad band). The resulting model consists of a t-J f-band
coupled via the Kondo exchange to the electrons in the broad band. allows for studying the f-electron delocalization transition. The result
is a doping-induced Mott transition for the f-electron delocalization, which we
demonstrate by density-matrix renormalization group (DMRG) calculations
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