7,543 research outputs found
Quantum states in a magnetic anti-dot
We study a new system in which electrons in two dimensions are confined by a
non homogeneous magnetic field. The system consists of a heterostructure with
on top of it a superconducting disk. We show that in this system electrons can
be confined into a dot region. This magnetic anti-dot has the interesting
property that the filling of the dot is a discrete function of the magnetic
field. The circulating electron current inside and outside the anti-dot can be
in opposite direction for certain bound states. And those states exhibit a
diamagnetic to paramagnetic transition with increasing magnetic field. The
absorption spectrum consists of many peaks, some of which violate Kohn's
theorem, and which is due to the coupling of the center of mass motion with the
other degrees of freedom.Comment: 6 pages, 12 ps figure
Resistance effects due to magnetic guiding orbits
The Hall and magnetoresistance of a two dimensional electron gas subjected to
a magnetic field barrier parallel to the current direction is studied as
function of the applied perpendicular magnetic field. The recent experimental
results of Nogaret {\em et al.} [Phys. Rev. Lett. {\bf 84}, 2231 (2000)] for
the magneto- and Hall resistance are explained using a semi-classical theory
based on the Landauer-B\"{u}ttiker formula. The observed positive
magnetoresistance peak is explained as due to a competition between a decrease
of the number of conducting channels as a result of the growing magnetic field,
from the fringe field of the ferromagnetic stripe as it becomes magnetized, and
the disappearance of snake orbits and the subsequent appearance of cycloidlike
orbits.Comment: 7 pages, 7 figure
Electron scattering on circular symmetric magnetic profiles in a two-dimensional electron gas
The quasi-bound and scattered states in a 2DEG subjected to a circular
symmetric steplike magnetic profile with zero average magnetic field are
studied. We calculate the effect of a random distribution of such identical
profiles on the transport properties of a 2DEG. We show that a nonzero Hall
resistance can be obtained, although , and that in some cases it
can even change sign as function of the Fermi energy or the magnetic field
strength. The Hall and magnetoresistance show pronounced resonances apart from
the Landau states of the inner core, corresponding to the so-called quasi-bound
snake orbit states.Comment: 7 pages, 8 figure
Prevalence of Rabbit Hemorrhagic Disease (RHD) in wild rabbits (Oryctolagus cuniculus) in Flanders, Belgium, 1999-2002
During the period of July 1999 through June 2002, carcasses of wild rabbits that had been shot or found dead and livers originating from wild rabbits that had been shot for consumption were collected in Flanders. One hundred and twelve carcasses were suitable for necropsy and histological and bacteriological analysis; histological analysis was possible in 41 livers. Considering the 112 rabbit carcasses only, Rabbit Hemorrhagic Disease (RHD) was found to be present in 33.9% of the cases. RHD was the most prevalent wild rabbit pathology detected in this study, before staphylococcosis (12.5%), and myxomatosis (10.7%). None of the liver samples from rabbits shot for consumption were positive for RHD. Of the 38 histologically RHD positive samples, 24 were analyzed with the hemagglutination (HA) technique, yielding 58.3% positive results. Seven samples that were histologically positive for RHD but HA negative were examined by transmission electron microscopy and were found positive for calicivirus. This proves that HA-negative RHD strains are circulating in the Flemish wild rabbit population
Adsorption of H2O, NH3, CO, NO2, and NO on graphene: A first-principles study
Motivated by the recent realization of graphene sensors to detect individual
gas molecules, we investigate the adsorption of H2O, NH3, CO, NO2, and NO on a
graphene substrate using first-principles calculations. The optimal adsorption
position and orientation of these molecules on the graphene surface is
determined and the adsorption energies are calculated. Molecular doping, i.e.
charge transfer between the molecules and the graphene surface, is discussed in
light of the density of states and the molecular orbitals of the adsorbates.
The efficiency of doping of the different molecules is determined and the
influence of their magnetic moment is discussed.Comment: 6 pages, 6 figure
Spin-orbit interaction induced singularity of the charge density relaxation propagator
The charge density relaxation propagator of a two dimensional electron
system, which is the slope of the imaginary part of the polarization function,
exhibits singularities for bosonic momenta having the order of the spin-orbit
momentum and depending on the momentum orientation. We have provided an
intuitive understanding for this non-analytic behavior in terms of the inter
chirality subband electronic transitions, induced by the combined action of
Bychkov-Rashba (BR) and Dresselhaus (D) spin-orbit coupling. It is shown that
the regular behavior of the relaxation propagator is recovered in the presence
of only one BR or D spin-orbit field or for spin-orbit interaction with equal
BR and D coupling strengths. This creates a new possibility to influence
carrier relaxation properties by means of an applied electric field.Comment: 4 figure
Spiral graphone and one sided fluorographene nano-ribbons
The instability of a free-standing one sided hydrogenated/fluorinated
graphene nano-ribbon, i.e. graphone/fluorographene, is studied using ab-initio,
semiempirical and large scale molecular dynamics simulations. Free standing
semi-infinite arm-chair like hydrogenated/fluorinated graphene (AC-GO/AC-GF)
and boat like hydrogenated/fluorinated graphene (B-GO/B-GF) (nano-ribbons which
are periodic along the zig-zag direction) are unstable and spontaneously
transform into spiral structures. We find that rolled, spiral B-GO and B-GF are
energetically more favorable than spiral AC-GO and AC-GF which is opposite to
the double sided flat hydrogenated/fluorinated graphene, i.e.
graphane/fluorographene. We found that the packed, spiral structures exhibit
unexpected localized HOMO-LUMO at the edges with increasing energy gap during
rolling. These rolled hydrocarbon structures are stable beyond room temperature
up to at least =1000\,K.Comment: Phys. Rev. B 87, 075448 (2013
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