12,907 research outputs found
Signatures of orbital loop currents in the spatially resolved local density of states
Polarized neutron scattering measurements have suggested that intra-unit cell
antiferromagnetism may be associated with the pseudogap phase. Assuming that
loop current order is responsible for the observed magnetism, we calculate some
signatures of such circulating currents in the local density of states around a
single non-magnetic impurity in a coexistence phase with superconductivity. We
find a distinct C4 symmetry breaking near the disorder which is also detectable
in the resulting quasi-particle interference patterns.Comment: 5 pages, 3 figure
Physical mechanism for a kinetic energy driven zero-bias anomaly in the Anderson-Hubbard model
The combined effects of strong disorder, strong correlations and hopping in
the Anderson-Hubbard model have been shown to produce a zero bias anomaly which
has an energy scale proportional to the hopping and minimal dependence on
interaction strength, disorder strength and doping. Disorder-induced
suppression of the density of states for a purely local interaction is
inconsistent with both the Efros-Shklovskii Coulomb gap and the
Altshuler-Aronov anomaly, and moreover the energy scale of this anomaly is
inconsistent with the standard energy scales of both weak and strong coupling
pictures. We demonstrate that a density of states anomaly with similar features
arises in an ensemble of two-site systems, and we argue that the energy scale t
emerges in strongly correlated systems with disorder due to the mixing of lower
and upper Hubbard orbitals on neighboring sites.Comment: 4 pages, 3 figures; new version includes minor changes to figures and
text to increase clarit
Atmospheric chemistry of gas-phase polycyclic aromatic hydrocarbons: formation of atmospheric mutagens.
The atmospheric chemistry of the 2- to 4-ring polycyclic aromatic hydrocarbons (PAH), which exist mainly in the gas phase in the atmosphere, is discussed. The dominant loss process for the gas-phase PAH is by reaction with the hydroxyl radical, resulting in calculated lifetimes in the atmosphere of generally less than one day. The hydroxyl (OH) radical-initiated reactions and nitrate (NO3) radical-initiated reactions often lead to the formation of mutagenic nitro-PAH and other nitropolycyclic aromatic compounds, including nitrodibenzopyranones. These atmospheric reactions have a significant effect on ambient mutagenic activity, indicating that health risk assessments of combustion emissions should include atmospheric transformation products
Robustness of the nodal d-wave spectrum to strongly fluctuating competing order
We resolve an existing controversy between, on the one hand, convincing
evidence for the existence of competing order in underdoped cuprates, and, on
the other hand, spectroscopic data consistent with a seemingly homogeneous
d-wave superconductor in the very same compounds. Specifically, we show how
short-range fluctuations of the competing order essentially restore the nodal
d-wave spectrum from the qualitatively distinct folded dispersion resulting
from homogeneous coexisting phases. The signatures of the fluctuating competing
order can be found mainly in a splitting of the antinodal quasi-particles and,
depending of the strength of the competing order, also in small induced nodal
gaps as found in recent experiments on underdoped La{2-x}SrxCuO4.Comment: 5 pages, 4 figure
Temperature dependence of the zero-bias anomaly in the Anderson-Hubbard model: Insights from an ensemble of two-site systems
Motivated by experiments on doped transition metal oxides, this paper
considers the interplay of interactions, disorder, kinetic energy and
temperature in a simple system. An ensemble of two-site Anderson-Hubbard model
systems has already been shown to display a zero-bias anomaly which shares
features with that found in the two-dimensional Anderson-Hubbard model. Here
the temperature dependence of the density of states of this ensemble is
examined. In the atomic limit, there is no zero-bias anomaly at zero
temperature, but one develops at small nonzero temperatures. With hopping,
small temperatures augment the zero-temperature kinetic-energy-driven zero-bias
anomaly, while at larger temperatures the anomaly is filled in.Comment: 8 pages, 3 figures; submitted to SCES 2010 conference proceeding
Many-Impurity Effects in Fourier Transform Scanning Tunneling Spectroscopy
Fourier transform scanning tunneling spectroscopy (FTSTS) is a useful
technique for extracting details of the momentum-resolved electronic band
structure from inhomogeneities in the local density of states due to
disorder-related quasiparticle scattering. To a large extent, current
understanding of FTSTS is based on models of Friedel oscillations near isolated
impurities. Here, a framework for understanding many-impurity effects is
developed based on a systematic treatment of the variance Delta rho^2(q,omega)
of the Fourier transformed local density of states rho(q,\omega). One important
consequence of this work is a demonstration that the poor signal-to-noise ratio
inherent in rho(q,omega) due to randomness in impurity positions can be
eliminated by configuration averaging Delta rho^2(q,omega). Furthermore, we
develop a diagrammatic perturbation theory for Delta rho^2(q,omega) and show
that an important bulk quantity, the mean-free-path, can be extracted from
FTSTS experiments.Comment: 7 pages, 5 figures. A version of the paper with high resolution,
colour figures is available at
http://www.trentu.ca/physics/batkinson/FTSTS.ps.gz minor revisions in
response to refree report + figure 5 is modifie
Influence of a Realistic Multiorbital Band Structure on Conducting Domain Walls in Perovskite Ferroelectrics
Domain wall morphologies in ferroelectrics are believed to be largely shaped
by electrostatic forces. Here, we show that for conducting domain walls, the
morphology also depends on the details of the charge-carrier band structure.
For concreteness, we focus on transition-metal perovskites like BaTiO and
SrTiO. These have a triplet of orbitals attached to the Ti atoms
that form the conduction bands when electron doped. We solve a set of coupled
equations -- Landau-Ginzburg-Devonshire (LGD) equations for the polarization,
tight-binding Schr\"odinger equations for the electron bands, and Gauss' law
for the electric potential -- to obtain polarization and electron density
profiles as a function of electron density. We find that at low electron
densities, the electron gas is pinned to the surfaces of the ferroelectric by a
Kittel-like domain structure. As the electron density increases, the domain
wall evolves smoothly through a zigzag head-to-head structure, eventually
becoming a flat head-to-head domain wall at high density. We find that the
Kittel-like morphology is protected by orbital asymmetry at low electron
densities, while at large electron densities the high density of states of the
multiorbital band structure provides effective screening of depolarizing fields
and flattens the domain wall relative to single-orbital models. Finally, we
show that in the zigzag phase, the electron gas develops tails that extend away
from the domain wall, in contrast to na\"{i}ve expectations.Comment: 17 pages, 13 figure
Effect of nonlocal interactions on the disorder-induced zero-bias anomaly in the Anderson-Hubbard model
To expand the framework available for interpreting experiments on disordered
strongly correlated systems, and in particular to explore further the
strong-coupling zero-bias anomaly found in the Anderson-Hubbard model, we ask
how this anomaly responds to the addition of nonlocal electron-electron
interactions. We use exact diagonalization to calculate the single-particle
density of states of the extended Anderson-Hubbard model. We find that for weak
nonlocal interactions the form of the zero-bias anomaly is qualitatively
unchanged. The energy scale of the anomaly continues to be set by an effective
hopping amplitude renormalized by the nonlocal interaction. At larger values of
the nonlocal interaction strength, however, hopping ceases to be a relevant
energy scale and higher energy features associated with charge correlations
dominate the density of states.Comment: 9 pages, 7 figure
An integrable multicomponent quad equation and its Lagrangian formulation
We present a hierarchy of discrete systems whose first members are the
lattice modified Korteweg-de Vries equation, and the lattice modified
Boussinesq equation. The N-th member in the hierarchy is an N-component system
defined on an elementary plaquette in the 2-dimensional lattice. The system is
multidimensionally consistent and a Lagrangian which respects this feature,
i.e., which has the desirable closure property, is obtained.Comment: 10 page
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