10,282 research outputs found
Dynamically generated dimension reduction and crossover in a spin orbital model
We study a spin orbital model in which the spin-spin interaction couples
linearly to the orbital isospin. Fluctuations drive the transition from
paramagnetic state to C type ordered state into a strongly first order one, as
observed in . At T=0, there is a FOCS to FOGS transition. Close to the
transition point, the system shows dynamically generated dimension reduction
and crossover, resulting in one or more spin reentrant transitions.Comment: Submitted to PRL. 4 pages and one figur
Charge Ordered RVB States in the Doped Cuprates
We study charge ordered d-wave resonating valence bond states (dRVB) in the
doped cuprates, and estimate the energies of these states in a generalized model by using a renormalized mean field theory. The long range Coulomb
potential tends to modulate the charge density in favor of the charge ordered
RVB state. The possible relevance to the recently observed
checkerboard patterns in tunnelling conductance in high cuprates is
discussed.Comment: 4 pages, 4 figures, 3 table
Quantum Critical Spin-2 Chain with Emergent SU(3) Symmetry
We study the quantum critical phase of a SU(2) symmetric spin-2 chain
obtained from spin-2 bosons in a one-dimensional lattice. We obtain the scaling
of the entanglement entropy and finite-size energies by exact diagonalization
and density-matrix renormalization group methods. From the numerical results of
the energy spectrum, central charge, and scaling dimension we identify the
conformal field theory describing the whole critical phase to be the SU(3)
Wess-Zumino-Witten model. We find that while in the whole critical phase the
Hamiltonian is only SU(2) invariant, there is an emergent SU(3) symmetry in the
thermodynamic limit
Coercive Field and Magnetization Deficit in Ga(1-x)Mn(x)As Epilayers
We have studied the field dependence of the magnetization in epilayers of the
diluted magnetic semiconductor Ga(1-x)Mn(x)As for 0.0135 < x < 0.083.
Measurements of the low temperature magnetization in fields up to 3 T show a
significant deficit in the total moment below that expected for full saturation
of all the Mn spins. These results suggest that the spin state of the
non-ferromagnetic Mn spins is energetically well separated from the
ferromagnetism of the bulk of the spins. We have also studied the coercive
field (Hc) as a function of temperature and Mn concentration, finding that Hc
decreases with increasing Mn concentration as predicted theoretically.Comment: 15 total pages -- 5 text, 1 table, 4 figues. Accepted for publication
in MMM 2002 conference proceedings (APL
Effect of pmma-mwnts loading on Co2 separation performance of thin film nanocomposite membrane
Nanocomposite membrane, especially the thin film nanocomposite (TFN) fabricated via interfacial polymerization (IP) is a relatively new class of membrane which features good separation performance and practical processing. This study investigated on the effects of multi-walled carbon nanotubes (MWNTs) loading on the gas separation performance of the resultant TFNs. TFNs were tested with pure CO2, N2 and CH4 gases at feed pressure of 2 bar. The findings from this study suggested that the optimum fillers loading was around 0.25 g/L in the coating solution which gives TFN with CO2 permeance of 53.5 gas permeation unit (GPU) (12% higher than base membrane without filler), CO2/N2 selectivity of 61 and CO2/CH4 selectivity of 35. The enhancement in CO2 permeance without sacrificing the membrane selectvities was attributed to the good dispersion and compatibility of the MWNTs with the polymer matrix while the nanotubes serve as rapid diffusion channels to facilitate transport of gases. TFN embedded with polymethyl methacrylate (PMMA)-MWNTs showed potential for low pressure carbon capture and storage application
Phase Structure of Compact Star in Modified Quark-Meson Coupling Model
The K condensation and quark deconfinement phase transitions are
investigated in the modified quark-meson coupling model. It is shown that K
condensation is suppressed because of the quark deconfinement when
202.2MeV, where is the bag constant for unpaired quark matter.
With the equation of state (EOS) solved self-consistently, we discuss the
properties of compact stars. We find that the EOS of pure hadron matter with
condensed K phase should be ruled out by the redshift for star EXO0748-676,
while EOS containing unpaired quark matter phase with being about
180MeV could be consistent with this observation and the best measured mass of
star PSR 1913+16. We then probe into the change of the phase structures in
possible compact stars with deconfinment phase as the central densities
increase. But if the recent inferred massive star among Terzan 5 with
M1.68M is confirmed, all the present EOSes with condensed phase
and deconfined phase would be ruled out and therefore these exotic phases are
unlikely to appear within neutron stars.Comment: 11 pages, 5 figure
Is There a Peccei-Quinn Phase Transition?
The nature of axion cosmology is usually said to depend on whether the
Peccei-Quinn (PQ) symmetry breaks before or after inflation. The PQ symmetry
itself is believed to be an accident, so there is not necessarily a symmetry
during inflation at all. We explore these issues in some simple models, which
provide examples of symmetry breaking before and after inflation, or in which
there is no symmetry during inflation and no phase transition at all. One
effect of these observations is to relax the constraints from isocurvature
fluctuations due to the axion during inflation. We also observe new
possibilities for evading the constraints due to cosmic strings and domain
walls, but they seem less generic.Comment: 14 pages. Several references adde
Atmospheric and Solar Neutrino Masses from Horizontal U(1) Symmetry
We study the neutrino mass matrix in supersymmetric models in which the quark
and charged lepton mass hierarchies and also the suppression of baryon or
lepton number violating couplings are all explained by horizontal
symmetry. It is found that the neutrino masses and mixing angles suggested by
recent atmospheric and solar neutrino experiments arise naturally in this
framework which fits in best with gauge-mediated supersymmetry breaking with
large . This framework highly favors the small angle MSW oscillation
of solar neutrinos, and determine the order of magnitudes of all the neutrino
mixing angles and mass hierarchies.Comment: No figures. 14 pages, revte
Localization of Bulk Matters on a Thick Anti-de Sitter Brane
In this paper, we investigate the localization and the mass spectra of
gravity and various bulk matter fields on a thick anti-de Sitter (AdS) brane,
by presenting the mass-independent potentials of the Kaluza-Klein (KK) modes in
the corresponding Schr\"{o}dinger equations. For gravity, the potential of the
KK modes tends to infinity at the boundaries of the extra dimension, which
leads to an infinite number of the bound KK modes. Although the gravity zero
mode cannot be localized on the AdS brane, the massive modes are trapped on the
brane. The scalar perturbations of the thick AdS brane have been analyzed, and
the brane is stable under the scalar perturbations. For spin-0 scalar fields
and spin-1 vector fields, the potentials of the KK modes also tend to infinity
at the boundaries of the extra dimension, and the characteristic of the
localization is the same as the case of gravity. For spin-1/2 fermions, by
introducing the usual Yukawa coupling with the
positive coupling constant , the four-dimensional massless left-chiral
fermion and massive Dirac fermions are obtained on the AdS thick brane.Comment: 23 pages, 9 figure
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