19,611 research outputs found
Electronic Structure of Hyperkagome Na4Ir3O8
We investigate the electronic structure of the frustrated magnet Na4Ir3O8
using density functional theory. Due to strong spin-orbit coupling, the
hyperkagome lattice is characterized by a half-filled complex of states, making
it a cubic iridium analogue of the high temperature superconducting cuprates.
The implications of our results for this unique material are discussed.Comment: expanded discussion with extra figures - 6 pages, 10 figure
Spin Hamiltonian of Hyperkagome Na4Ir3O8
We derive the spin Hamiltonian for the quantum spin liquid Na4Ir3O8, and then
estimate the direct and superexchange contributions between near neighbor
iridium ions using a tight binding parametrization of the electronic structure.
We find a magnitude of the exchange interaction comparable to experiment for a
reasonable value of the on-site Coulomb repulsion. For one of the two tight
binding parametrizations we have studied, the direct exchange term, which is
isotropic, dominates the total exchange. This provides support for those
theories proposed to describe this novel quantum spin liquid that assume an
isotropic Heisenberg model.Comment: 9 pages, 4 figure
Light Quark Mass Reweighting
We present a systematic study of the effectiveness of light quark mass
reweighting. This method allows a single lattice QCD ensemble, generated with a
specific value of the dynamical light quark mass, to be used to determine
results for other, nearby light dynamical quark masses. We study two gauge
field ensembles generated with 2+1 flavors of dynamical domain wall fermions
with light quark masses m_l=0.02 (m_\pi=620 MeV) and m_l=0.01 (m_\pi=420 MeV).
We reweight each ensemble to determine results which could be computed directly
from the other and check the consistency of the reweighted results with the
direct results. The large difference between the 0.02 and 0.01 light quark
masses suggests that this is an aggressive application of reweighting as can be
seen from fluctuations in the magnitude of the reweighting factor by four
orders of magnitude. Never-the-less, a comparison of the reweighed topological
charge, average plaquette, residual mass, pion mass, pion decay constant, and
scalar correlator between these two ensembles shows agreement well described by
the statistical errors. The issues of the effective number of configurations
and finite sample size bias are discussed. An examination of the topological
charge distribution implies that it is more favorable to reweight from heavier
mass to lighter quark mass.Comment: 24 pages and 10 figure
Hot Spots on the Fermi Surface of Bi2212: Stripes versus Superstructure
In a recent paper Saini et al. have reported evidence for a pseudogap around
(pi,0) at room temperature in the optimally doped superconductor Bi2212. This
result is in contradiction with previous ARPES measurements. Furthermore they
observed at certain points on the Fermi surface hot spots of high spectral
intensity which they relate to the existence of stripes in the CuO planes. They
also claim to have identified a new electronic band along Gamma-M1 whose one
dimensional character provides further evidence for stripes. We demonstrate in
this Comment that all the measured features can be simply understood by
correctly considering the superstructure (umklapp) and shadow bands which occur
in Bi2212.Comment: 1 page, revtex, 1 encapsulated postscript figure (color
Extraction of the Electron Self-Energy from Angle Resolved Photoemission Data: Application to Bi2212
The self-energy , the fundamental function which
describes the effects of many-body interactions on an electron in a solid, is
usually difficult to obtain directly from experimental data. In this paper, we
show that by making certain reasonable assumptions, the self-energy can be
directly determined from angle resolved photoemission data. We demonstrate this
method on data for the high temperature superconductor
(Bi2212) in the normal, superconducting, and pseudogap phases.Comment: expanded version (6 pages), to be published, Phys Rev B (1 Sept 99
Photon Conserving Radiative Transfer around Point Sources in multi-dimensional Numerical Cosmology
Many questions in physical cosmology regarding the thermal and ionization
history of the intergalactic medium are now successfully studied with the help
of cosmological hydrodynamical simulations. Here we present a numerical method
that solves the radiative transfer around point sources within a three
dimensional cartesian grid. The method is energy conserving independently of
resolution: this ensures the correct propagation speeds of ionization fronts.
We describe the details of the algorithm, and compute as first numerical
application the ionized region surrounding a mini-quasar in a cosmological
density field at z=7.Comment: 5 pages, 4 figures, submitted to ApJ
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