4,625 research outputs found
Mott transitions in two-orbital Hubbard systems
We investigate the Mott transitions in two-orbital Hubbard systems. Applying
the dynamical mean field theory and the self-energy functional approach, we
discuss the stability of itinerant quasi-particle states in each band. It is
shown that separate Mott transitions occur at different Coulomb interaction
strengths in general. On the other hand, if some special conditions are
satisfied for the interactions, spin and orbital fluctuations are equally
enhanced at low temperatures, resulting in a single Mott transition. The phase
diagrams are obtained at zero and finite temperatures. We also address the
effect of the hybridization between two orbitals, which induces the Kondo-like
heavy fermion states in the intermediate orbital-selective Mott phase.Comment: 21 Pages, 17 Figures, to appear in Progress of Theoretical Physics
(YKIS2004 Proceedings
Zero-temperature Phase Diagram of Two Dimensional Hubbard Model
We investigate the two-dimensional Hubbard model on the triangular lattice
with anisotropic hopping integrals at half filling. By means of a self-energy
functional approach, we discuss how stable the non-magnetic state is against
magnetically ordered states in the system. We present the zero-temperature
phase diagram, where the normal metallic state competes with magnetically
ordered states with and structures. It is shown
that a non-magnetic Mott insulating state is not realized as the ground state,
in the present framework, but as a meta-stable state near the magnetically
ordered phase with structure.Comment: 4 pages, 4 figure
First-order quantum phase transition in the orthogonal-dimer spin chain
We investigate the low-energy properties of the orthogonal-dimer spin chain
characterized by a frustrated dimer-plaquette structure. When the competing
antiferromagnetic couplings are varied, the first-order quantum phase
transition occurs between the dimer and the plaquette phases, which is
accompanied by nontrivial features due to frustration: besides the
discontinuity in the lowest excitation gap at the transition point, a sharp
level-crossing occurs for the spectrum in the plaquette phase. We further
reveal that the plateau in the magnetization curve at 1/4 of the full moment
dramatically changes its character in the vicinity of the critical point. It is
argued that the first-order phase transition in this system captures some
essential properties found in the two-dimensional orthogonal-dimer model
proposed for .Comment: 7 pages, submitted to Phys. Rev.
Dust coagulation and fragmentation in a collapsing cloud core and their influence on non-ideal magnetohydrodynamic effects
We determine the time evolution of the dust particle size distribution during
the collapse of a cloud core, accounting for both dust coagulation and dust
fragmentation, to investigate the influence of dust growth on non-ideal
magnetohydrodynamic effects.The density evolution of the collapsing core is
given by a one-zone model. We assume two types of dust model: dust composed
only of silicate (silicate dust) and dust with a surface covered by
ice ( ice dust). When only considering
collisional coagulation, the non-ideal magnetohydrodynamic effects are not
effective in the high-density region for both the silicate and
ice dust cases. This is because dust coagulation reduces the
abundance of small dust particles, resulting in less efficient adsorption of
charged particles on the dust surface. For the silicate dust case, when
collisional fragmentation is included, the non-ideal magnetohydrodynamic
effects do apply at a high density of $n_{\mathrm{H}}>10^{12} \
\mathrm{cm^{-3}}\mathrm{H_{2}O}\mathrm{H_{2}O}n_{\mathrm{H}}\gtrsim 10^{14} \ \mathrm{cm^{-3}}$, even when
collisional fragmentation is considered. Our results suggest that it is
necessary to consider both dust collisional coagulation and fragmentation to
activate non-ideal magnetohydrodynamic effects, which should play a significant
role in the star and disk formation processes.Comment: Accepted for publication in MNRAS. 17 pages, 11 figure
Proposal for a two-channel quantum dot setup: Prediction for the capacitance lineshape
We have made a detailed proposal for a two-channel quantum dot setup. The
energy scales in the problem are such that we are able to make connection with
the two-channel Anderson model, which, in spite of being well-known in the
context of heavy-Fermion systems remained theoretically elusive until recently
and lacked a mesoscopic realization. Verification of our precise and robust
predictions for the differential capacitance lineshape of the dot will provide
an experimental signature of the two-channel behavior.Comment: Proceedings for SCES conference (2005
Orbital-selective Mott transitions in the anisotropic two-band Hubbard model at finite temperatures
The anisotropic degenerate two-orbital Hubbard model is studied within
dynamical mean-field theory at low temperatures. High-precision calculations on
the basis of a refined quantum Monte Carlo (QMC) method reveal that two
distinct orbital-selective Mott transitions occur for a bandwidth ratio of 2
even in the absence of spin-flip contributions to the Hund exchange. The second
transition -- not seen in earlier studies using QMC, iterative perturbation
theory, and exact diagonalization -- is clearly exposed in a low-frequency
analysis of the self-energy and in local spectra.Comment: 4 pages, 5 figure
Phase diagram of a frustrated mixed-spin ladder with diagonal exchange bonds
Using exact numerical diagonalization and the conformal field theory
approach, we study the effect of magnetic frustrations due to diagonal exchange
bonds in a system of two coupled mixed-spin Heisenberg chains. It
is established that relatively moderate frustrations are able to destroy the
ferrimagnetic state and to stabilize the critical spin-liquid phase typical for
half-integer-spin antiferromagnetic Heisenberg chains. Both phases are
separated by a narrow but finite region occupied by a critical
partially-polarized ferromagnetic phase.Comment: 5 PRB pages, 7 eps figures, to appear in Phys. Rev.
Chronic Hepatitis B and C Co-Infection Increased All-Cause Mortality in HAART-Naive HIV Patients in Northern Thailand
A total of 755 highly active antiretroviral therapy (HAART)-naive HIV-infected patients were enrolled at a government hospital in Thailand from 1 June 2000 to 15 October 2002. Census date of survival was on 31 October 2004 or the date of HAART initiation. Of 700 (92.6%) patients with complete data, the prevalence of hepatitis B virus (HBV) surface antigen and anti-hepatitis C virus (HCV) antibody positivity was 11.9% and 3.3%, respectively. Eight (9.6%) HBV co-infected patients did not have anti-HBV core antibody (anti-HBcAb). During 1166.7 person-years of observation (pyo), 258 (36.9%) patients died [22.1/100 pyo, 95% confidence interval (CI) 16.7–27.8]. HBV and probably HCV co-infection was associated with a higher mortality with adjusted hazard ratios (aHRs) of 1.81 (95% CI 1.30–2.53) and 1.90 (95% CI 0.98–3.69), respectively. Interestingly, HBV co-infection without anti-HBc Ab was strongly associated with death (aHR 6.34, 95% CI 3.99–10.3). The influence of hepatitis co-infection on the natural history of HAART-naive HIV patients requires greater attention
Universal properties from local geometric structure of Killing horizon
We consider universal properties that arise from a local geometric structure
of a Killing horizon. We first introduce a non-perturbative definition of such
a local geometric structure, which we call an asymptotic Killing horizon. It is
shown that infinitely many asymptotic Killing horizons reside on a common null
hypersurface, once there exists one asymptotic Killing horizon. The
acceleration of the orbits of the vector that generates an asymptotic Killing
horizon is then considered. We show that there exists the
or sub-algebra on an asymptotic Killing horizon
universally, which is picked out naturally based on the behavior of the
acceleration. We also argue that the discrepancy between string theory and the
Euclidean approach in the entropy of an extreme black hole may be resolved, if
the microscopic states responsible for black hole thermodynamics are connected
with asymptotic Killing horizons.Comment: 14 pages, v2. minor correction
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