2,386 research outputs found

### Field dependent quasiparticles in the infinite dimensional Hubbard model

We present dynamical mean field theory (DMFT) results for the local spectral
densities of the one- and two-particle response functions for the infinite
dimensional Hubbard model in a magnetic field. We look at the different regimes
corresponding to half-filling, near half-filling and well away from
half-filling, for intermediate and strong values of the local interaction $U$.
The low energy results are analyzed in terms of quasiparticles with field
dependent parameters. The renormalized parameters are determined by two
different methods, both based on numerical renormalization group (NRG)
calculations, and we find good agreement. Away from half-filling the
quasiparticle weights, $z_\sigma(H)$, differ according to the spin type
$\sigma=\uparrow$ or $\sigma=\downarrow$. Using the renormalized parameters, we
show that DMFT-NRG results for the local longitudinal and transverse dynamic
spin susceptibilities in an arbitrary field can be understood in terms of
repeated scattering of these quasiparticles. We also check Luttinger's theorem
for the Hubbard model and find it to be satisfied in all parameter regimes and
for all values of the magnetic field.Comment: 14 pages, 21 figure

### Magnetic Field Effects on Quasiparticles in Strongly Correlated Local Systems

We show that quasiparticles in a magnetic field of arbitrary strength $H$ can
be described by field dependent parameters. We illustrate this approach in the
case of an Anderson impurity model and use the numerical renormalization group
(NRG) to calculate the renormalized parameters for the levels with spin
$\sigma$, $\tilde\epsilon_{\mathrm{d},\sigma}(H)$, resonance width
$\tilde\Delta(H)$ and the effective local quasiparticle interaction $\tilde
U(H)$. In the Kondo or strong correlation limit of the model the progressive
de-renormalization of the quasiparticles can be followed as the magnetic field
is increased. The low temperature behaviour, including the conductivity, in
arbitrary magnetic field can be calculated in terms of the field dependent
parameters using the renormalized perturbation expansion. Using the NRG the
field dependence of the spectral density on higher scales is also calculated.Comment: 15 pages, 17 figure

### Renormalized parameters and perturbation theory for an n-channel Anderson model with Hund's rule coupling: Asymmetric case

We explore the predictions of the renormalized perturbation theory for an
n-channel Anderson model, both with and without Hund's rule coupling, in the
regime away from particle-hole symmetry. For the model with n=2 we deduce the
renormalized parameters from numerical renormalization group calculations, and
plot them as a function of the occupation at the impurity site, nd. From these
we deduce the spin, orbital and charge susceptibilities, Wilson ratios and
quasiparticle density of states at T=0, in the different parameter regimes,
which gives a comprehensive overview of the low energy behavior of the model.
We compare the difference in Kondo behaviors at the points where nd=1 and nd=2.
One unexpected feature of the results is the suppression of the charge
susceptibility in the strong correlation regime over the occupation number
range 1 <nd <3.Comment: 9 pages, 17 figure

### Dynamic response functions for the Holstein-Hubbard model

We present results on the dynamical correlation functions of the
particle-hole symmetric Holstein-Hubbard model at zero temperature, calculated
using the dynamical mean field theory which is solved by the numerical
renormalization group method. We clarify the competing influences of the
electron-electron and electron-phonon interactions particularity at the
different metal to insulator transitions. The Coulomb repulsion is found to
dominate the behaviour in large parts of the metallic regime. By suppressing
charge fluctuations, it effectively decouples electrons from phonons. The
phonon propagator shows a characteristic softening near the metal to
bipolaronic transition but there is very little softening on the approach to
the Mott transition.Comment: 13 pages, 19 figure

### High-order current correlation functions in Kondo systems

We examine the statistics of current fluctuations in a junction with a
quantum dot described by Kondo Hamiltonian. With the help of modified Keldish
technique we calculate the third current cumulant. As a function of ratio
$v=eV/T_{K}$ the 3rd cumulant was obtained for three different regimes: Fermi
liquid regime (v>1). Unlike
the case of noninteracting dot, 3rd cumulant shows strong non-linear voltage
dependence. Only in the asymptotical limit of large voltages the linear
dependence on $V$ is recovered.Comment: 5 pages, 2 figure

### Model of Quantum Criticality in He3 bilayers Adsorbed on graphite

Recent experiments on He3 bilayers adsorbed on Graphite have shown striking
quantum critical properties at the point where the first layer localizes. We
model this system with the Anderson lattice plus inter-layer Coulomb repulsion
in two dimensions. Assuming that quantum critical fluctuations come from a
vanishing of the effective hybridization, we can reproduce several features of
the system, including the apparent occurrence of two quantum critical points
(QCP), the variation of the effective mass and coherence temperature with
coverage.Comment: 4 pages, 2 figures, new version as published on PRL, journal
reference and DOI adde

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