34 research outputs found
Electronic Structure of Disclinated Graphene in an Uniform Magnetic Field
The electronic structure in the vicinity of the 1-heptagonal and 1-pentagonal
defects in the carbon graphene plane is investigated. Using a continuum gauge
field-theory model the local density of states around the Fermi energy is
calculated for both cases. In this model, the disclination is represented by an
SO(2) gauge vortex and corresponding metric follows from the elasticity
properties of the graphene membrane. To enhance the interval of energies, a
self-consistent perturbation scheme is used. The Landau states are investigated
and compared with the predicted values.Comment: keywords: graphene, heptagonal defect, elasticity, carbon nanohorns,
13 page
Effective action for strongly correlated electron systems
The su(2|1) coherent-state path-integral representation of the partition
function of the t - J model of strongly correlated electrons is derived at
finite doping. The emergent effective action is compared to the one proposed
earlier on phenomenological grounds by Shankar to describe holes in an
antiferromagnet (Nucl.Phys. B330 (1990) 433). The t - J model effective action
is found to have an important "extra" factor with no analogue in Shankar's
action. It represents the local constraint of no double electron occupancy and
reflects the rearrangement of the underlying phase-space manifold due to the
presence of strong electron correlation. This important ingredient is shown to
be essential to describe the physics of strongly correlated electron systems.
Keywords: t - J model of strongly correlated electrons; su(2|1)
coherent-state path integralComment: 22 page
Fluctuations and Dissipation of Coherent Magnetization
A quantum mechanical model is used to derive a generalized Landau-Lifshitz
equation for a magnetic moment, including fluctuations and dissipation. The
model reproduces the Gilbert-Brown form of the equation in the classical limit.
The magnetic moment is linearly coupled to a reservoir of bosonic degrees of
freedom. Use of generalized coherent states makes the semiclassical limit more
transparent within a path-integral formulation. A general
fluctuation-dissipation theorem is derived. The magnitude of the magnetic
moment also fluctuates beyond the Gaussian approximation. We discuss how the
approximate stochastic description of the thermal field follows from our
result. As an example, we go beyond the linear-response method and show how the
thermal fluctuations become anisotropy-dependent even in the uniaxial case.Comment: 22 page