1,685 research outputs found
Entanglement witnessing in superconducting beamsplitters
We analyse a large class of superconducting beamsplitters for which the Bell
parameter (CHSH violation) is a simple function of the spin detector
efficiency. For these superconducting beamsplitters all necessary information
to compute the Bell parameter can be obtained in Y-junction setups for the
beamsplitter. Using the Bell parameter as an entanglement witness, we propose
an experiment which allows to verify the presence of entanglement in Cooper
pair splitters.Comment: 5 pages, 2 figures, accepted for publication in EP
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
Creating exotic condensates via quantum-phase-revival dynamics in engineered lattice potentials
In the field of ultracold atoms in optical lattices a plethora of phenomena
governed by the hopping energy and the interaction energy have been
studied in recent years. However, the trapping potential typically present in
these systems sets another energy scale and the effects of the corresponding
time scale on the quantum dynamics have rarely been considered. Here we study
the quantum collapse and revival of a lattice Bose-Einstein condensate (BEC) in
an arbitrary spatial potential, focusing on the special case of harmonic
confinement. Analyzing the time evolution of the single-particle density
matrix, we show that the physics arising at the (temporally) recurrent quantum
phase revivals is essentially captured by an effective single particle theory.
This opens the possibility to prepare exotic non-equilibrium condensate states
with a large degree of freedom by engineering the underlying spatial lattice
potential.Comment: 9 pages, 6 figure
One-parameter Superscaling at the Metal-Insulator Transition in Three Dimensions
Based on the spectral statistics obtained in numerical simulations on three
dimensional disordered systems within the tight--binding approximation, a new
superuniversal scaling relation is presented that allows us to collapse data
for the orthogonal, unitary and symplectic symmetry () onto a
single scaling curve. This relation provides a strong evidence for
one-parameter scaling existing in these systems which exhibit a second order
phase transition. As a result a possible one-parameter family of spacing
distribution functions, , is given for each symmetry class ,
where is the dimensionless conductance.Comment: 4 pages in PS including 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
Magnetism and d-wave superconductivity on the half-filled square lattice with frustration
The role of frustration and interaction strength on the half-filled Hubbard
model is studied on the square lattice with nearest and next-nearest neighbour
hoppings t and t' using the Variational Cluster Approximation (VCA). At
half-filling, we find two phases with long-range antiferromagnetic (AF) order:
the usual Neel phase, stable at small frustration t'/t, and the so-called
collinear (or super-antiferromagnet) phase with ordering wave-vector
or , stable for large frustration. These are separated by a phase with
no detectable long-range magnetic order. We also find the d-wave
superconducting (SC) phase (), which is favoured by frustration if
it is not too large. Intriguingly, there is a broad region of coexistence where
both AF and SC order parameters have non-zero values. In addition, the physics
of the metal-insulator transition in the normal state is analyzed. The results
obtained with the help of the VCA method are compared with the large-U
expansion of the Hubbard model and known results for the frustrated J1-J2
Heisenberg model. These results are relevant for pressure studies of undoped
parents of the high-temperature superconductors: we predict that an insulator
to d-wave SC transition may appear under pressure.Comment: 12 pages, 10 figure
Critical Level Statistics in Two-dimensional Disordered Electron Systems
The level statistics in the two dimensional disordered electron systems in
magnetic fields (unitary ensemble) or in the presence of strong spin-orbit
scattering (symplectic ensemble) are investigated at the Anderson transition
points. The level spacing distribution functions 's are found to be
independent of the system size or of the type of the potential distribution,
suggesting the universality. They behave as in the small region in
the former case, while rise is seen in the latter.Comment: LaTeX, to be published in J. Phys. Soc. Jpn. (Letter) Nov., Figures
will be sent on reques
Does a magnetic field modify the critical behaviour at the metal-insulator transition in 3-dimensional disordered systems?
The critical behaviour of 3-dimensional disordered systems with magnetic
field is investigated by analyzing the spectral fluctuations of the energy
spectrum. We show that in the thermodynamic limit we have two different
regimes, one for the metallic side and one for the insulating side with
different level statistics. The third statistics which occurs only exactly at
the critical point is {\it independent} of the magnetic field. The critical
behaviour which is determined by the symmetry of the system {\it at} the
critical point should therefore be independent of the magnetic field.Comment: 10 pages, Revtex, 4 PostScript figures in uuencoded compressed tar
file are appende
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