1,358 research outputs found
Renormalization-group study of a magnetic impurity in a Luttinger liquid
A generalized Anderson model for a magnetic impurity in an interacting
one-dimensional electron gas is studied via a mapping onto a classical Coulomb
gas. For weak potential scattering, the local-moment parameter regime expands
as repulsive bulk interactions become stronger, but the Kondo scale for the
quenching of the impurity moment varies nonmonotonically. There also exist two
regimes dominated by backward potential scattering: one in which the impurity
is nonmagnetic, and another in which an unquenched local moment survives down
to very low temperatures.Comment: REVTeX, 4 pages, 3 epsf-embedded EPS figure
Does Luttinger liquid behaviour survive in an atomic wire on a surface?
We form a highly simplified model of an atomic wire on a surface by the
coupling of two one-dimensional chains, one with electron-electron interactions
to represent the wire and and one with no electron-electron interactions to
represent the surface. We use exact diagonalization techniques to calculate the
eigenstates and response functions of our model, in order to determine both the
nature of the coupling and to what extent the coupling affects the Luttinger
liquid properties we would expect in a purely one-dimensional system. We find
that while there are indeed Luttinger liquid indicators present, some residual
Fermi liquid characteristics remain.Comment: 14 pages, 7 figures. Submitted to J Phys
Phase diagram of an asymmetric spin ladder
We investigate an asymmetric zig-zag spin ladder with different exchange
integrals on both legs using bosonization and renormalization group. When the
leg exchange integrals and frustration both are sufficiently small,
renormalization group analysis shows that the Heisenberg critical point flows
to an intermediate-coupling fixed point with gapless excitations and a
vanishing spin velocity. When they are large, a spin gap opens and a dimer
liquid is realized. Here, we find a continuous manifold of Hamiltonians with
dimer product ground states, interpolating between the Majumdar-Ghosh and
sawtooth spin-chain model.Comment: 4 pages, 2 EPS figures, to be published in PR
Tomonaga-Luttinger parameters for doped Mott insulators
The Tomonaga--Luttinger parameter determines the critical behavior
in quasi one-dimensional correlated electron systems, e.g., the exponent
for the density of states near the Fermi energy. We use the numerical
density-matrix renormalization group method to calculate from the
slope of the density-density correlation function in momentum space at zero
wave vector. We check the accuracy of our new approach against exact results
for the Hubbard and XXZ Heisenberg models. We determine in the phase
diagram of the extended Hubbard model at quarter filling, , and
confirm the bosonization results on the critical
line and at infinitesimal doping of the
charge-density-wave (CDW) insulator for all interaction strengths. The doped
CDW insulator exhibits exponents only for small doping and strong
correlations.Comment: 7 pages, 4 figure
An Exactly Solvable Kondo Problem for Interacting One-Dimensional Fermions
The single impurity Kondo problem in the one-dimensional -potential
Fermi gas is exactly solved for two sets of special coupling constants via
Bethe ansatz. It is found that ferromagnetic Kondo screening does occur in one
case which confirms the Furusaki-Nagaosa conjecture while in the other case it
does not, which we explain in a simple physical picture. The surface energy,
the low temperature specific heat and the Pauli susceptibility induced by the
impurity and thereby the Kondo temperature are derived explicitly.Comment: 8 pages, LATEX, REVTE
Friedel oscillations in a gas of interacting one-dimensional fermionic atoms confined in a harmonic trap
Using an asymptotic phase representation of the particle density operator
in the one-dimensional harmonic trap, the part which describes the Friedel oscillations is extracted. The
expectation value with respect to the interacting
ground state requires the calculation of the mean square average of a properly
defined phase operator. This calculation is performed analytically for the
Tomonaga-Luttinger model with harmonic confinement. It is found that the
envelope of the Friedel oscillations at zero temperature decays with the
boundary exponent away from the classical boundaries. This
value differs from that known for open boundary conditions or strong pinning
impurities. The soft boundary in the present case thus modifies the decay of
Friedel oscillations. The case of two components is also discussed.Comment: Revised version to appear in Journal of Physics B: Atomic, Molecular
and Optical Physic
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Plasmodium knowlesi: a superb in vivo nonhuman primate model of antigenic variation in malaria.
Antigenic variation in malaria was discovered in Plasmodium knowlesi studies involving longitudinal infections of rhesus macaques (M. mulatta). The variant proteins, known as the P. knowlesi Schizont Infected Cell Agglutination (SICA) antigens and the P. falciparum Erythrocyte Membrane Protein 1 (PfEMP1) antigens, expressed by the SICAvar and var multigene families, respectively, have been studied for over 30 years. Expression of the SICA antigens in P. knowlesi requires a splenic component, and specific antibodies are necessary for variant antigen switch events in vivo. Outstanding questions revolve around the role of the spleen and the mechanisms by which the expression of these variant antigen families are regulated. Importantly, the longitudinal dynamics and molecular mechanisms that govern variant antigen expression can be studied with P. knowlesi infection of its mammalian and vector hosts. Synchronous infections can be initiated with established clones and studied at multi-omic levels, with the benefit of computational tools from systems biology that permit the integration of datasets and the design of explanatory, predictive mathematical models. Here we provide an historical account of this topic, while highlighting the potential for maximizing the use of P. knowlesi - macaque model systems and summarizing exciting new progress in this area of research
Perturbation theory for optical excitations in the one-dimensional extended Peierls--Hubbard model
For the one-dimensional, extended Peierls--Hubbard model we calculate
analytically the ground-state energy and the single-particle gap to second
order in the Coulomb interaction for a given lattice dimerization. The
comparison with numerically exact data from the Density-Matrix Renormalization
Group shows that the ground-state energy is quantitatively reliable for Coulomb
parameters as large as the band width. The single-particle gap can almost
triple from its bare Peierls value before substantial deviations appear. For
the calculation of the dominant optical excitations, we follow two approaches.
In Wannier theory, we perturb the Wannier exciton states to second order. In
two-step perturbation theory, similar in spirit to the GW-BSE approach, we form
excitons from dressed electron-hole excitations. We find the Wannier approach
to be superior to the two-step perturbation theory. For singlet excitons,
Wannier theory is applicable up to Coulomb parameters as large as half band
width. For triplet excitons, second-order perturbation theory quickly fails
completely.Comment: 32 pages, 12 figures, submtted to JSTA
Effect of nearest neighbor repulsion on the low frequency phase diagram of a quarter-filled Hubbard-Holstein chain
We have studied the influence of nearest-neighbor (NN) repulsion on the low
frequency phase diagram of a quarter-filled Hubbard-Holstein chain. The NN
repulsion term induces the apparition of two new long range ordered phases (one
CDW for positive and one CDW for
negative ) that did not exist in the V=0 phase diagram. These results
are put into perspective with the newly observed charge ordered phases in
organic conductors and an interpretation of their origin in terms of
electron-molecular vibration coupling is suggested.Comment: 10 pages, 10 figure
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