1,953 research outputs found
Random dispersion approximation for the Hubbard model
We use the Random Dispersion Approximation (RDA) to study the Mott-Hubbard
transition in the Hubbard model at half band filling. The RDA becomes exact for
the Hubbard model in infinite dimensions. We implement the RDA on finite chains
and employ the Lanczos exact diagonalization method in real space to calculate
the ground-state energy, the average double occupancy, the charge gap, the
momentum distribution, and the quasi-particle weight. We find a satisfactory
agreement with perturbative results in the weak- and strong-coupling limits. A
straightforward extrapolation of the RDA data for lattice results in
a continuous Mott-Hubbard transition at . We discuss the
significance of a possible signature of a coexistence region between insulating
and metallic ground states in the RDA that would correspond to the scenario of
a discontinuous Mott-Hubbard transition as found in numerical investigations of
the Dynamical Mean-Field Theory for the Hubbard model.Comment: 10 pages, 11 figure
Reconciliation or Racialization? Contemporary Discourses about Residential Schools in the Canadian Prairies
The residential school system is one of the darkest examples of Canada’s colonial policy. Education about the residential schools is believed to be the path to reconciliation; that is, the restoration of equality between Aboriginal and non-Aboriginal peoples in Canada. While the acquisition of the long-ignored history of residential schools has the potential to centre marginalized perspectives and narratives, knowledge acquisition alone is not necessarily a reconciliatory endeavour. The critical discourse analysis offered in this article reveals how dominant narratives about residential schools, cited by well-meaning educators, re-inscribe harmful colonial subjectivities about Aboriginal peoples. Through a post-structural lens and drawing from interviews conducted across one prairie province, I demonstrate how citing popular, contemporary discourses about residential schools continues to racialize Aboriginal peoples while positioning non-Aboriginal peoples as supportive and historically conscious. Readers are brought to think about how learning about residential schools for reconciliation might be approached as the disruption of subjectivities and the refusal to (re)pathologize Aboriginal peoples. Otherwise, efforts at reconciliation risk re-inscribing the racism that justified residential schools in their inception.
Fourth-Order Perturbation Theory for the Half-Filled Hubbard Model in Infinite Dimensions
We calculate the zero-temperature self-energy to fourth-order perturbation
theory in the Hubbard interaction for the half-filled Hubbard model in
infinite dimensions. For the Bethe lattice with bare bandwidth , we compare
our perturbative results for the self-energy, the single-particle density of
states, and the momentum distribution to those from approximate analytical and
numerical studies of the model. Results for the density of states from
perturbation theory at agree very well with those from the Dynamical
Mean-Field Theory treated with the Fixed-Energy Exact Diagonalization and with
the Dynamical Density-Matrix Renormalization Group. In contrast, our results
reveal the limited resolution of the Numerical Renormalization Group approach
in treating the Hubbard bands. The momentum distributions from all approximate
studies of the model are very similar in the regime where perturbation theory
is applicable, . Iterated Perturbation Theory overestimates the
quasiparticle weight above such moderate interaction strengths.Comment: 19 pages, 17 figures, submitted to EPJ
Strong-coupling approach to the Mott--Hubbard insulator on a Bethe lattice in Dynamical Mean-Field Theory
We calculate the Hubbard bands for the half-filled Hubbard model on a Bethe
lattice with infinite coordination number up to and including third order in
the inverse Hubbard interaction. We employ the Kato--Takahashi perturbation
theory to solve the self-consistency equation of the Dynamical Mean-Field
Theory analytically for the single-impurity Anderson model in multi-chain
geometry. The weight of the secondary Hubbard sub-bands is of fourth order so
that the two-chain geometry is sufficient for our study. Even close to the
Mott--Hubbard transition, our results for the Mott--Hubbard gap agree very well
with those from numerical Dynamical Density-Matrix Renormalization Group
(DDMRG) calculations. The density of states of the lower Hubbard band also
agrees very well with DDMRG data, apart from a resonance contribution at the
upper band edge which cannot be reproduced in low-order perturbation theory.Comment: 40 pages, 7 figure
Application of the Density Matrix Renormalization Group in momentum space
We investigate the application of the Density Matrix Renormalization Group
(DMRG) to the Hubbard model in momentum-space. We treat the one-dimensional
models with dispersion relations corresponding to nearest-neighbor hopping and
hopping and the two-dimensional model with isotropic nearest-neighbor
hopping. By comparing with the exact solutions for both one-dimensional models
and with exact diagonalization in two dimensions, we first investigate the
convergence of the ground-state energy. We find variational convergence of the
energy with the number of states kept for all models and parameter sets. In
contrast to the real-space algorithm, the accuracy becomes rapidly worse with
increasing interaction and is not significantly better at half filling. We
compare the results for different dispersion relations at fixed interaction
strength over bandwidth and find that extending the range of the hopping in one
dimension has little effect, but that changing the dimensionality from one to
two leads to lower accuracy at weak to moderate interaction strength. In the
one-dimensional models at half-filling, we also investigate the behavior of the
single-particle gap, the dispersion of spinon excitations, and the momentum
distribution function. For the single-particle gap, we find that proper
extrapolation in the number of states kept is important. For the spinon
dispersion, we find that good agreement with the exact forms can be achieved at
weak coupling if the large momentum-dependent finite-size effects are taken
into account for nearest-neighbor hopping. For the momentum distribution, we
compare with various weak-coupling and strong-coupling approximations and
discuss the importance of finite-size effects as well as the accuracy of the
DMRG.Comment: 15 pages, 11 eps figures, revtex
Analytical and Numerical Treatment of the Mott--Hubbard Insulator in Infinite Dimensions
We calculate the density of states in the half-filled Hubbard model on a
Bethe lattice with infinite connectivity. Based on our analytical results to
second order in , we propose a new `Fixed-Energy Exact Diagonalization'
scheme for the numerical study of the Dynamical Mean-Field Theory. Corroborated
by results from the Random Dispersion Approximation, we find that the gap opens
at . Moreover, the density of states near the gap
increases algebraically as a function of frequency with an exponent
in the insulating phase. We critically examine other analytical
and numerical approaches and specify their merits and limitations when applied
to the Mott--Hubbard insulator.Comment: 22 pages, 16 figures; minor changes (one reference added, included
comparison with Falicov-Kimball model
Mott-Hubbard transition in infinite dimensions
We calculate the zero-temperature gap and quasiparticle weight of the
half-filled Hubbard model with a random dispersion relation. After
extrapolation to the thermodynamic limit, we obtain reliable bounds on these
quantities for the Hubbard model in infinite dimensions. Our data indicate that
the Mott-Hubbard transition is continuous, i.e., that the quasiparticle weight
becomes zero at the same critical interaction strength at which the gap opens.Comment: 4 pages, RevTeX, 5 figures included with epsfig Final version for
PRL, includes L=14 dat
Utilization of Polyspecific Antiserum for Specific Radioimmunoassays: Radioimmunoassays for Rat Fetuin and Bikunin Were Developed by Using Antiserum Against Total Rat Serum Proteins
Polyspecific antiserum against total rat serum proteins was used to develop specific and sensitive radioimmunoassays for fetuin and bikunin, two minor protein components of rat plasma. The radioimmunoassays proved to be highly useful to trace bikunin and fetuin in the course of developing isolation procedures, since neither specific functional assays nor monospecific antisera were available. The two examples demonstrate that, in general, it will be possible to develop a specific and sensitive radioimmunoassay with antiserum raised against a crude antigen preparation, such as a body fluid or a tissue extract, provided that a minute amount of pure antigen is available for preparing the radioiodinated antigen
- …