2,179 research outputs found
Sensitivity of the magnetic state of a spin lattice on itinerant electron orbital phase
Spatially extended localized spins can interact via indirect exchange
interaction through Friedel oscillations in the Fermi sea. In arrays of
localized spins such interaction can lead to a magnetically ordered phase.
Without external magnetic field such a phase is well understood via a
"two-impurity" Kondo model. Here we employ non-equilibrium transport
spectroscopy to investigate the role of the orbital phase of conduction
electrons on the magnetic state of a spin lattice. We show experimentally, that
even tiniest perpendicular magnetic field can influence the magnitude of the
inter-spin magnetic exchange.Comment: To be published in PhysicaE EP2DS proceedin
Litter drives ecosystem and plant community changes in cattail invasion
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/116913/1/eap2009192398.pd
Fano effect and Kondo effect in quantum dots formed in strongly coupled quantum wells
We present lateral transport measurements on strongly, vertically coupled
quantum dots formed in separate quantum wells in a GaAs/AlGaAs heterostructure.
Coulomb oscillations are observed forming a honeycomb lattice consistent with
two strongly coupled dots. When the tunnel barriers in the upper well are
reduced we observe the Fano effect due to the interfering paths through a
resonant state in the lower well and a continuum state in the upper well. In
both regimes an in plane magnetic field reduces the coupling between the wells
when the magnetic length is comparable to the center to center separation of
the wells. We also observe the Kondo effect which allows the spin states of the
double dot system to be probed.Comment: 4 pages, 5 figure
Generalized Forward-Backward Splitting with Penalization for Monotone Inclusion Problems
We introduce a generalized forward-backward splitting method with penalty
term for solving monotone inclusion problems involving the sum of a finite
number of maximally monotone operators and the normal cone to the nonempty set
of zeros of another maximal monotone operator. We show weak ergodic convergence
of the generated sequence of iterates to a solution of the considered monotone
inclusion problem, provided the condition corresponded to the Fitzpatrick
function of the operator describing the set of the normal cone is fulfilled.
Under strong monotonicity of an operator, we show strong convergence of the
iterates. Furthermore, we utilize the proposed method for minimizing a
large-scale hierarchical minimization problem concerning the sum of
differentiable and nondifferentiable convex functions subject to the set of
minima of another differentiable convex function. We illustrate the
functionality of the method through numerical experiments addressing
constrained elastic net and generalized Heron location problems
Positrons from Primordial Black Hole Microquasars and Gamma-ray Bursts
We propose several novel scenarios how capture of small sublunar-mass
primordial black holes (PBHs) by compact stars, white dwarfs or neutron stars,
can lead to distinct short gamma-ray bursts (sGRBs) as well as microquasars
(MQs). In addition to providing new signatures, relativistic jets from these
systems will accelerate positrons to high energies. We find that if PBHs
constitute a sizable fraction of DM, they can significantly contribute to the
excess observed in the positron flux by the Pamela, the AMS-02 and the
Fermi-LAT experiments. Our proposal combines the beneficial features of
astrophysical sources and dark matter.Comment: 9 pages, 2 figures, v2: significant revisions, published version,
Physics Letters B (2018
Probing spin-charge separation in a Tomonaga-Luttinger liquid
In a one-dimensional (1D) system of interacting electrons, excitations of
spin and charge travel at different speeds, according to the theory of a
Tomonaga-Luttinger Liquid (TLL) at low energies. However, the clear observation
of this spin-charge separation is an ongoing challenge experimentally. We have
fabricated an electrostatically-gated 1D system in which we observe spin-charge
separation and also the predicted power-law suppression of tunnelling into the
1D system. The spin-charge separation persists even beyond the low-energy
regime where the TLL approximation should hold. TLL effects should therefore
also be important in similar, but shorter, electrostatically gated wires, where
interaction effects are being studied extensively worldwide.Comment: 11 pages, 4 PDF figures, uses scicite.sty, Science.bs
Possible effect of collective modes in zero magnetic field transport in an electron-hole bilayer
We report single layer resistivities of 2-dimensional electron and hole gases
in an electron-hole bilayer with a 10nm barrier. In a regime where the
interlayer interaction is stronger than the intralayer interaction, we find
that an insulating state () emerges at or
lower, when both the layers are simultaneously present. This happens deep in
the metallic" regime, even in layers with , thus making
conventional mechanisms of localisation due to disorder improbable. We suggest
that this insulating state may be due to a charge density wave phase, as has
been expected in electron-hole bilayers from the Singwi-Tosi-Land-Sj\"olander
approximation based calculations of L. Liu {\it et al} [{\em Phys. Rev. B},
{\bf 53}, 7923 (1996)]. Our results are also in qualitative agreement with
recent Path-Integral-Monte-Carlo simulations of a two component plasma in the
low temperature regime [ P. Ludwig {\it et al}. {\em Contrib. Plasma Physics}
{\bf 47}, No. 4-5, 335 (2007)]Comment: 5 pages + 3 EPS figures (replaced with published version
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