12,073 research outputs found
Absence of a true long-range orbital order in a two-leg Kondo ladder
We investigate, through the density-matrix renormalization group and the
Lanczos technique, the possibility of a two-leg Kondo ladder present an
incommensurate orbital order. Our results indicate a staggered short-range
orbital order at half-filling. Away from half-filling our data are consistent
with an incommensurate quasi-long-range orbital order. We also observed that an
interaction between the localized spins enhances the rung-rung current
correlations.Comment: 7 pages, 6 figures, changed the introduction and added some
discussion
Coexistence of Pairing Tendencies and Ferromagnetism in a Doped Two-Orbital Hubbard Model on Two-Leg Ladders
Using the Density Matrix Renormalization Group and two-leg ladders, we
investigate an electronic two-orbital Hubbard model including plaquette
diagonal hopping amplitudes. Our goal is to search for regimes where charges
added to the undoped state form pairs, presumably a precursor of a
superconducting state.For the electronic density , i.e. the undoped
limit, our investigations show a robust antiferromagnetic ground
state, as in previous investigations. Doping away from and for large
values of the Hund coupling , a ferromagnetic region is found to be stable.
Moreover, when the interorbital on-site Hubbard repulsion is smaller than the
Hund coupling, i.e. for in the standard notation of multiorbital Hubbard
models, our results indicate the coexistence of pairing tendencies and
ferromagnetism close to . These results are compatible with previous
investigations using one dimensional systems. Although further research is
needed to clarify if the range of couplings used here is of relevance for real
materials, such as superconducting heavy fermions or pnictides, our theoretical
results address a possible mechanism for pairing that may be active in the
presence of short-range ferromagnetic fluctuations.Comment: 8 pages, 4 Fig
Defect-dependent colossal negative thermal expansion in UiO-66(Hf) metal-organic framework
Thermally-densified hafnium terephthalate UiO-66(Hf) is shown to exhibit the
strongest isotropic negative thermal expansion (NTE) effect yet reported for a
metal-organic framework (MOF). Incorporation of correlated vacancy defects
within the framework affects both the extent of thermal densification and the
magnitude of NTE observed in the densified product. We thus demonstrate that
defect inclusion can be used to tune systematically the physical behaviour of a
MOF.Comment: 8 pages, 4 figures, revise
Current noise through a Kondo quantum dot in a SU(N) Fermi liquid state
The current noise through a mesoscopic quantum dot is calculated and analyzed
in the Fermi liquid regime of the SU(N) Kondo model. Results connect the
Johnson-Nyquist noise to the shot noise for an arbitrary ratio of voltage and
temperature, and show that temperature corrections are sizeable in usual
experiments. For the experimentally relevant SU(4) case, quasiparticle
interactions are shown to increase the shot noise.Comment: 4 pages, 2 figures, to be published in Phys. Rev. Lett. (revised
version
New method for obtaining complex roots in the semiclassical coherent-state propagator formula
A semiclassical formula for the coherent-state propagator requires the
determination of specific classical paths inhabiting a complex phase-space
through a Hamiltonian flux. Such trajectories are constrained to special
boundary conditions which render their determination difficult by common
methods. In this paper we present a new method based on Runge-Kutta integrator
for a quick, easy and accurate determination of these trajectories. Using
nonlinear one dimensional systems we show that the semiclassical formula is
highly accurate as compared to its exact counterpart . Further we clarify how
the phase of the semiclassical approximation is correctly retrieved under time
evolution.Comment: 8 pages, 4 figures. Submitted to Brazilian Journal of Physic
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