949 research outputs found
Spectral Density of the Two-Impurity Anderson Model
We investigate static and dynamical ground-state properties of the
two-impurity Anderson model at half filling in the limit of vanishing impurity
separation using the dynamical density-matrix renormalization group method. In
the weak-coupling regime, we find a quantum phase transition as function of
inter-impurity hopping driven by the charge degrees of freedom. For large
values of the local Coulomb repulsion, the transition is driven instead by a
competition between local and non-local magnetic correlations. We find evidence
that, in contrast to the usual phenomenological picture, it seems to be the
bare effective exchange interactions which trigger the observed transition.Comment: 18 pages, 6 figures, submitted to J. Phys.:Condens. Matte
Optical Conductivity of the Trellis-Lattice t-J Model: Charge Fluctuations in NaV_2O_5
Optical conductivity of the trellis lattice t-J model at quarter filling is
calculated by an exact-diagonalization technique on small clusters, whereby the
valence state of V ions of NaV_2O_5 is considered. We show that the
experimental features at \sim 1 eV, including peak positions, presence of
shoulders, and anisotropic spectral weight, can be reproduced in reasonable
range of parameter values, only by assuming that the system is in the charge
disproportionated ground state. Possible reconciliation with experimental data
suggesting the presence of uniform ladders at T>T_c is discussed.Comment: 4 pages, 4 gif figures. Minor revisions have been made. Hardcopies of
figures (or the entire manuscript) can be obtained by e-mail request to
[email protected]
Correlation function for the one-dimensional extended Hubbard model at quarter filling
We examine the density-density correlation function in the Tomonaga-Luttinger
liquid state for the one-dimensional extended Hubbard model with the on-site
Coulomb repulsion and the intersite repulsion at quarter filling. By
taking into account the effect of the marginally irrelevant umklapp scattering
operator by utilizing the renormalization-group technique based on the
bosonization method, we obtain the generalized analytical form of the
correlation function. We show that, in the proximity to the gapped
charge-ordered phase, the correlation function exhibits anomalous crossover
between the pure power-law behavior and the power-law behavior with logarithmic
corrections, depending on the length scale. Such a crossover is also confirmed
by the highly-accurate numerical density-matrix renormalization group method.Comment: 6 pages, 3 figure
Kitaev interactions between j=1/2 moments in honeycomb Na2IrO3 are large and ferromagnetic: insights from ab initio quantum chemistry calculations
NaIrO, a honeycomb 5 oxide, has been recently identified as a
potential realization of the Kitaev spin lattice. The basic feature of this
spin model is that for each of the three metal-metal links emerging out of a
metal site, the Kitaev interaction connects only spin components perpendicular
to the plaquette defined by the magnetic ions and two bridging ligands. The
fact that reciprocally orthogonal spin components are coupled along the three
different links leads to strong frustration effects and nontrivial physics.
While the experiments indicate zigzag antiferromagnetic order in NaIrO,
the signs and relative strengths of the Kitaev and Heisenberg interactions are
still under debate. Herein we report results of ab initio many-body electronic
structure calculations and establish that the nearest-neighbor exchange is
strongly anisotropic with a dominant ferromagnetic Kitaev part, whereas the
Heisenberg contribution is significantly weaker and antiferromagnetic. The
calculations further reveal a strong sensitivity to tiny structural details
such as the bond angles. In addition to the large spin-orbit interactions, this
strong dependence on distortions of the IrO plaquettes singles out the
honeycomb 5 oxides as a new playground for the realization of
unconventional magnetic ground states and excitations in extended systems.Comment: 13 pages, 2 tables, 3 figures, accepted in NJ
Particular solutions of a certain class of associated Cauchy-Euler fractional partial differential equations via fractional calculus
Prominent 5d-orbital contribution to the conduction electrons in gold
We have examined the valence-band electronic structures of gold and silver in
the same column in the periodic table with nominally filled d orbitals by means
of a recently developed polarization-dependent hard x-ray photoemission.
Contrary to a common expectation, it is found that the 5d-orbital electrons
contribute prominently to the conduction electrons in gold while the conduction
electrons in silver are to some extent free-electron-like with negligible 4d
contribution, which could be related to a well-known fact that gold is more
stable than silver in air. The 4d electron correlation effects are found to be
essential for the conduction electron character in silver.Comment: 8 pages, 4 figures, to be appeared in New J. Phys
Density-matrix renormalisation group approach to quantum impurity problems
A dynamic density-matrix renormalisation group approach to the spectral
properties of quantum impurity problems is presented. The method is
demonstrated on the spectral density of the flat-band symmetric single-impurity
Anderson model. We show that this approach provides the impurity spectral
density for all frequencies and coupling strengths. In particular, Hubbard
satellites at high energy can be obtained with a good resolution. The main
difficulties are the necessary discretisation of the host band hybridised with
the impurity and the resolution of sharp spectral features such as the
Abrikosov-Suhl resonance.Comment: 16 pages, 6 figures, submitted to Journal of Physics: Condensed
Matte
Landau mapping and Fermi liquid parameters of the 2D t-J model
We study the momentum distribution function n(k) in the 2D t-J model on small
clusters by exact diagonalization. We show that n(k) can be decomposed
systematically into two components with Bosonic and Fermionic doping
dependence. The Bosonic component originates from the incoherent motion of
holes and has no significance for the low energy physics. For the Fermionic
component we exlicitely perform the one-to-one Landau mapping between the low
lying eigenstates of the t-J model clusters and those of an equivalent system
of spin-1/2 quasiparticles. This mapping allows to extract the quasiparticle
dispersion, statistics, and Landau parameters. The results show conclusively
that the 2D t-J model for small doping is a Fermi liquid with a `small' Fermi
surface and a moderately strong attractive interaction between the
quasiparticles.Comment: Revtex file, 5 pages with 5 embedded eps-files, hardcopies of figures
(or the entire manuscript) can be obtained by e-mail request to:
[email protected]
Electronic States and Superconducting Transition Temperature based on the Tomonaga-Luttinger liquid in PrBaCuO
An NQR experiment revealed superconductivity of
PrBaCuO (Pr247) to be realized on CuO double chain
layers and suggests possibility of novel one-dimensional(1D) superconductivity.
To clarify the nature of the 1D superconductivity, we calculate the band
dispersions of Pr247 by using the generalized gradient approximation(GGA). It
indicates that Fermi surface of CuO double chains is well described to the
electronic structure of a quasi-1D system.
Assuming the zigzag Hubbard chain model to be an effective model of the
system, we derive tight binding parameters of the model from a fit to the
result of GGA. Based on the Tomonaga-Luttinger liquid theory, we estimate
transition temperature () of the quasi-1D zigzag Hubbard model from the
calculated value of the Luttinger liquid parameter . The result of
is consistent with that of experiments in Pr247 and it suggests that the
mechanism of the superconductivity is well understood within the concept of the
Tomonaga-Luttinger liquid.Comment: 4 pages, 5 figure
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