1,807 research outputs found
Metal-insulator transition caused by the coupling to localized charge-frustrated systems under ice-rule local constraint
We report the results of our theoretical and numerical study on electronic
and transport properties of fermion systems with charge frustration. We
consider an extended Falicov-Kimball model in which itinerant spinless fermions
interact repulsively by U with localized particles whose distribution satisfies
a local constraint under geometrical frustration, the so-called ice rule. We
numerically calculate the density of states, optical conductivity, and inverse
participation ratio for the models on the pyrochlore, checkerboard, and kagome
lattices, and discuss the nature of metal-insulator transitions at commensurate
fillings. As a result, we show that the ice-rule local constraint leads to
several universal features in the electronic structure; a charge gap opens at a
considerably small U compared to the bandwidth, and the energy spectrum
approaches a characteristic form in the large U limit, that is, the
noninteracting tight-binding form in one dimension or the -functional
peak. In the large U region, the itinerant fermions are confined in the
macroscopically-degenerate ice-rule configurations, which consist of a bunch of
one-dimensional loops: We call this insulating state the charge ice. On the
other hand, transport properties are much affected by the geometry and
dimensionality of lattices; e.g., the pyrochlore lattice model exhibits a
transition from a metallic to the charge-ice insulating state by increasing U,
while the checkerboard lattice model appears to show Anderson localization
before opening a gap. Meanwhile, in the kagome lattice case, we do not obtain
clear evidence of Anderson localization. Our results elucidate the universality
and diversity of phase transitions to the charge-ice insulator in fully
frustrated lattices.Comment: 16 pages, 17 figure
Generalized L\"uscher Formula in Multi-channel Baryon-Meson Scattering
L\"uscher's formula relates the elastic scattering phase shifts to the
two-particle energy levels in a finite cubic box. The original formula was
obtained for elastic scattering of two massive spinless particles in the center
of mass frame. In this paper, we consider the case for the scattering of a spin
1/2 particle with a spinless particle in multi-channel scattering. A
generalized relation between the energy of two particle system and the
scattering matrix elements is established. We first obtain this relation using
quantum-mechanics in both center-of-mass frame and in a general moving frame.
The result is then generalized to quantum field theory using methods outlined
in Ref. \cite{Hansen:2012tf}. We verify that the results obtained using both
methods are equivalent up to terms that are exponentially suppressed in the box
size.Comment: One reference adde
Evidence for hard chiral logarithms in quenched lattice QCD
We present the first direct evidence that quenched QCD differs from full QCD
in the chiral () limit, as predicted by chiral perturbation
theory, from our quenched lattice QCD simulations at . We
measured the spectrum of light hadrons on ,
and , using staggered quarks of masses ,
and . The pion masses showed clear evidence for logarithmic
violations of the PCAC relation , as predicted by
quenched chiral perturbation theory. The dependence on spatial lattice volume
precludes this being a finite size effect. No evidence was seen for such chiral
logarithms in the behaviour of the chiral condensate
.Comment: 10 pages, 4 figures, uuencoded compressed postscript fil
Numerical Study on Split Coil-shaped HTS Bulks to Improve the Field Homogeneity for Compact NMR Relaxometry Magnets
AbstractWe have been developing a new compact NMR magnet using stacked HTS bulks. In this pa er, in order to improve the trapped magnetic field homogeneity and to obtain the enlarged sample space of HTS bulk magnet for compact NMR relaxometry, the HTS bulk magnet with 10mm gap length in the center region of HTS bulk magnet (we call it “split coil-shaped THS bulks”) were proposed and studied as the functions of size and shape of HTS bulk using 3D FEM based electromagnetic analysis. The improved field homogeneity was obtained using notch coil shaped HTS bulk configuration and the field compensation by attached the coil instated of the bulks
Improvement Of A Beam-bending Viscosimeter For Fast Measurement
The beam-bending method is very useful for the viscosity determination of glasses, but the time spent to run the measurement is usually very long. The present note describes the performance of an improved beam-bending viscosimeter at the support stand and loading rod to get the faster measurements of high viscosity glasses with better reliability and precision. The testing time was reduced from 8 to less than 4 hours to run one measurement at three different temperatures (1100, 1200, and 1300°C), with the precision of almost one order of magnitude better (±0.01 for 1g η in poise).6593028302
Intra-Landau level polarization effect for a striped Hall gas
We calculate the polarization function including only intra-Landau level
correlation effects of striped Hall gas. Using the polarization function, the
dielectric function, the dispersion of the plasmon and the correlation energy
are computed in a random phase approximation (RPA) and generalized random phase
approximation (GRPA). The plasmon becomes anisotropic and gapless owing to the
anisotropy of the striped Hall gas and two dimensionality of the quantum Hall
system. The plasmon approximately agrees with the phonon derived before by the
single mode approximation. The (G)RPA correlation energy is compared with other
numerical calculations.Comment: 15 pages,15 figures, revtex4, published versio
- …