1,054 research outputs found
Quantum tunneling induced Kondo effect in single molecular magnets
We consider transport through a single-molecule magnet strongly coupled to
metallic electrodes. We demonstrate that for half-integer spin of the molecule
electron- and spin-tunneling \emph{cooperate} to produce both quantum tunneling
of the magnetic moment and a Kondo effect in the linear conductance. The Kondo
temperature depends sensitively on the ratio of the transverse and easy-axis
anisotropies in a non-monotonic way. The magnetic symmetry of the transverse
anisotropy imposes a selection rule on the total spin for the occurrence of the
Kondo effect which deviates from the usual even-odd alternation.Comment: 4 pages, 4 figure
Kondo-transport spectroscopy of single molecule magnets
We demonstrate that in a single molecule magnet (SMM) strongly coupled to
electrodes the Kondo effect involves all magnetic excitations. This Kondo
effect is induced by the quantum tunneling of the magnetic moment (QTM).
Importantly, the Kondo temperature can be much larger than the magnetic
splittings. We find a strong modulation of the Kondo effect as function of the
transverse anisotropy parameter or a longitudinal magnetic field. For both
integer and half-integer spin this can be used for an accurate transport
spectroscopy of the magnetic states in low magnetic fields on the order of the
easy-axis anisotropy parameter. We set up a relationship between the Kondo
effects for successive integer and half-integer spins.Comment: 5 pages, 3 figure
Nonequilibrium Spin Dynamics in the Ferromagnetic Kondo Model
Motivated by recent experiments on molecular quantum dots we investigate the
relaxation of pure spin states when coupled to metallic leads. Under suitable
conditions these systems are well described by a ferromagnetic Kondo model.
Using two recently developed theoretical approaches, the time-dependent
numerical renormalization group and an extended ow equation method, we
calculate the real-time evolution of a Kondo spin into its partially screened
steady state. We obtain exact analytical results which agree well with
numerical implementations of both methods. Analytical expressions for the
steady state magnetization and the dependence of the long-time relaxation on
microscopic parameters are established. We find the long-time relaxation
process to be much faster in the regime of anisotropic Kondo couplings. The
steady state magnetization is found to deviate significantly from its thermal
equilibrium value.Comment: 4 pages, 3 figures, final version as accepted by Physical Review
Letter
Stall- und weidebasierte Milchproduktionssysteme Analysen zur Lebensmittelkonversionseffizienz
Reducing the amount of human-edible feed in livestock diets is a key factor towards more sustainable livestock systems. Based on results from a conventional wholesystem study comparing performance, efficiency, land productivity, and profitability of an indoor-feeding system (SH) and a pasture-based dairy production system (VW) in lowlands of Central Switzerland, the net contribution of these systems to human food protein and energy supply was analysed. Depending on the presumed human-edible fraction, the system VW produced between 6.6 and 11.2 times more human-edible
protein and 3.5 to 6.6 times more human-edible energy via animal products than the animals consumed via feeds. For the group SH, these factors were clearly lower but still in a positive range (1.0 to 2.5 and 0.9 and 1.9 for protein and energy respectively). In addition, protein quality in the animal products was considerable higher than protein
quality in the potentially human-edible feed components
Magnetism and domain formation in SU(3)-symmetric multi-species Fermi mixtures
We study the phase diagram of an SU(3)-symmetric mixture of three-component
ultracold fermions with attractive interactions in an optical lattice,
including the additional effect on the mixture of an effective three-body
constraint induced by three-body losses. We address the properties of the
system in by using dynamical mean-field theory and variational Monte
Carlo techniques. The phase diagram of the model shows a strong interplay
between magnetism and superfluidity. In the absence of the three-body
constraint (no losses), the system undergoes a phase transition from a color
superfluid phase to a trionic phase, which shows additional particle density
modulations at half-filling. Away from the particle-hole symmetric point the
color superfluid phase is always spontaneously magnetized, leading to the
formation of different color superfluid domains in systems where the total
number of particles of each species is conserved. This can be seen as the SU(3)
symmetric realization of a more general tendency to phase-separation in
three-component Fermi mixtures. The three-body constraint strongly disfavors
the trionic phase, stabilizing a (fully magnetized) color superfluid also at
strong coupling. With increasing temperature we observe a transition to a
non-magnetized SU(3) Fermi liquid phase.Comment: 36 pages, 17 figures; Corrected typo
Partial Wave Analysis of Scattering with Nonlocal Aharonov-Bohm Effect and Anomalous Cross Section induced by Quantum Interference
Partial wave theory of a three dmensional scattering problem for an arbitray
short range potential and a nonlocal Aharonov-Bohm magnetic flux is
established. The scattering process of a ``hard shere'' like potential and the
magnetic flux is examined. An anomalous total cross section is revealed at the
specific quantized magnetic flux at low energy which helps explain the
composite fermion and boson model in the fractional quantum Hall effect. Since
the nonlocal quantum interference of magnetic flux on the charged particles is
universal, the nonlocal effect is expected to appear in quite general potential
system and will be useful in understanding some other phenomena in mesoscopic
phyiscs.Comment: 6 figure
Stall- und weidebasierte Milchproduktionssysteme Modellbetriebsanalysen zur Wirtschaftlichkeit unter österreichischen Produktionsbedingungen
In a whole-system study in lowland of Central Switzerland from 2007 - 2010 compared the performance, efficiency, land productivity and profitability of indoor-feeding (SH)
dairy production with that of pasture-based feeding (VW) dairy production. In the present study these experimental results were economically evaluated under Austrian
market und production conditions. Therefore conventional and organic model farms were created and analyzed using full cost accounting. In comparison to the barn feeding strategy a higher farm income, income per labor unit were achieved with the pasture-based feeding strategy. These economic differences were more pronounced under organic than conventional conditions
Level spacings at the metal-insulator transition in the Anderson Hamiltonians and multifractal random matrix ensembles
We consider orthogonal, unitary, and symplectic ensembles of random matrices
with (1/a)(ln x)^2 potentials, which obey spectral statistics different from
the Wigner-Dyson and are argued to have multifractal eigenstates. If the
coefficient is small, spectral correlations in the bulk are universally
governed by a translationally invariant, one-parameter generalization of the
sine kernel. We provide analytic expressions for the level spacing distribution
functions of this kernel, which are hybrids of the Wigner-Dyson and Poisson
distributions. By tuning the single parameter, our results can be excellently
fitted to the numerical data for three symmetry classes of the
three-dimensional Anderson Hamiltonians at the metal-insulator transition,
previously measured by several groups using exact diagonalization.Comment: 12 pages, 8 figures, REVTeX. Additional figure and text on the level
number variance, to appear in Phys.Rev.
Kondo effect and spin-active scattering in ferromagnet-superconductor junctions
We study the interplay of superconducting and ferromagnetic correlations on
charge transport in different geometries with a focus on both a quantum point
contact as well as a quantum dot in the even and the odd state with and without
spin-active scattering at the interface. In order to obtain a complete picture
of the charge transport we calculate the full counting statistics in all cases
and compare the results with experimental data. We show that spin-active
scattering is an essential ingredient in the description of quantum point
contacts. This holds also for quantum dots in an even charge state whereas it
is strongly suppressed in a typical Kondo situation. We explain this feature by
the strong asymmetry of the hybridisations with the quantum dot and show how
Kondo peak splitting in a magnetic field can be used for spin filtering. For
the quantum dot in the even state spin-active scattering allows for an
explanation of the experimentally observed mini-gap feature.Comment: 14 pages, 7 figures, accepted by PR
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