25,188 research outputs found
Adittional levels between Landau bands due to vacancies in graphene: towards a defect engineering
We describe the effects of vacancies on the electronic properties of a
graphene sheet in the presence of a perpendicular magnetic field: from a single
defect to an organized vacancy lattice. An isolated vacancy is the minimal
possible inner edge, showing an antidotlike behaviour, which results in an
extra level between consecutive Landau levels. Two close vacancies may couple
to each other, forming a vacancy molecule tuned by the magnetic field. We show
that a vacancy lattice introduce an extra band in between Landau levels with
localization properties that could lead to extra Hall resistance plateaus.Comment: 6 pages, 4 figures, few comments added after referees - accepted to
publication in Phys. Rev.
Valley polarization effects on the localization in graphene Landau levels
Effects of disorder and valley polarization in graphene are investigated in
the quantum Hall regime. We find anomalous localization properties for the
lowest Landau level (LL), where disorder can induce wavefunction delocalization
(instead of localization), both for white-noise and gaussian-correlated
disorder. We quantitatively identify the contribution of each sublattice to
wavefunction amplitudes. Following the valley (sublattice) polarization of
states within LLs for increasing disorder we show: (i) valley mixing in the
lowest LL is the main effect behind the observed anomalous localization
properties, (ii) the polarization suppression with increasing disorder depends
on the localization for the white-noise model, while, (iii) the disorder
induces a partial polarization in the higher Landau levels for both disorder
models.Comment: 5 pages, 6 figures, extended version, with 2 new figures adde
Slow relaxation and sensitivity to disorder in trapped lattice fermions after a quench
We consider a system of non-interacting fermions in one dimension subject to
a single-particle potential consisting of (a) a strong optical lattice, (b) a
harmonic trap, and (c) uncorrelated on-site disorder. After a quench, in which
the center of the harmonic trap is displaced, we study the occupation function
of the fermions and the time-evolution of experimental observables.
Specifically, we present numerical and analytical results for the post-quench
occupation function of the fermions, and analyse the time-evolution of the
real-space density profile. Unsurprisingly for a non-interacting (and therefore
integrable) system, the infinite-time limit of the density profile is
non-thermal. However, due to Bragg-localization of the higher-energy
single-particle states, the approach to even this non-thermal state is
extremely slow. We quantify this statement, and show that it implies a
sensitivity to disorder parametrically stronger than that expected from
Anderson localization.Comment: 15 pages, 11 figure
On the universal Representation of the Scattering Matrix of Affine Toda Field Theory
By exploiting the properties of q-deformed Coxeter elements, the scattering
matrices of affine Toda field theories with real coupling constant related to
any dual pair of simple Lie algebras may be expressed in a completely generic
way. We discuss the governing equations for the existence of bound states, i.e.
the fusing rules, in terms of q-deformed Coxeter elements, twisted q-deformed
Coxeter elements and undeformed Coxeter elements. We establish the precise
relation between these different formulations and study their solutions. The
generalized S-matrix bootstrap equations are shown to be equivalent to the
fusing rules. The relation between different versions of fusing rules and
quantum conserved quantities, which result as nullvectors of a doubly
q-deformed Cartan like matrix, is presented. The properties of this matrix
together with the so-called combined bootstrap equations are utilised in order
to derive generic integral representations for the scattering matrix in terms
of quantities of either of the two dual algebras. We present extensive
case-by-case data, in particular on the orbits generated by the various Coxeter
elements.Comment: 57 page
Inner and outer edge states in graphene rings: A numerical investigation
We numerically investigate quantum rings in graphene and find that their
electronic properties may be strongly influenced by the geometry, the edge
symmetries and the structure of the corners. Energy spectra are calculated for
different geometries (triangular, hexagonal and rhombus-shaped graphene rings)
and edge terminations (zigzag, armchair, as well as the disordered edge of a
round geometry). The states localized at the inner edges of the graphene rings
describe different evolution as a function of magnetic field when compared to
those localized at the outer edges. We show that these different evolutions are
the reason for the formation of sub-bands of edge states energy levels,
separated by gaps (anticrossings). It is evident from mapping the charge
densities that the anticrossings occur due to the coupling between inner and
outer edge states.Comment: 8 pages, 7 figures. Figures in low resolution due to size
requirements - higher quality figures on reques
Resonant tunneling through protected quantum dots at phosphorene edges
We theoretically investigate phosphorene zigzag nanorribons as a platform for
constriction engineering. In the presence of a constriction at the upper edge,
quantum confinement of edge protected states reveals resonant tunnelling
Breit-Wigner transmission peaks, if the upper edge is uncoupled to the lower
edge. Coupling between edges in thin constrictions gives rise to Fano-like and
anti-resonances in the transmission spectrum of the system.Comment: 8 pages,7 figure
Differential Emission Measure Determination of Collisionally Ionized Plasma: II. Application to Hot Stars
In a previous paper we have described a technique to derive constraints on
the differential emission measure (DEM) distribution, a measure of the
temperature distribution, of collisionally ionized hot plasmas from their X-ray
emission line spectra. We apply this technique to the Chandra/HETG spectra of
all of the nine hot stars available to us at the time this project was
initiated. We find that DEM distributions of six of the seven O stars in our
sample are very similar but that theta Ori has an X-ray spectrum characterized
by higher temperatures. The DEM distributions of both of B stars in our sample
have lower magnitudes than those of the O stars and one, tau Sco, is
characterized by higher temperatures than the other, beta Cru. These results
confirm previous work in which high temperatures have been found for theta Ori
and tau Sco and taken as evidence for channeling of the wind in magnetic
fields, the existence of which are related to the stars' youth. Our results
demonstrate the utility of our method for deriving temperature information for
large samples of X-ray emission line spectra.Comment: The contents of this paper were formerly part of astro-ph/0403603
which was split into two paper
Investigations on alternative substances for control of apple scab - results from sanitation trials
The intention of this research project, which was supported within the "Bundesprogramm Ă–kologischer
Landbau", was to look for alternatives in organic fruit growing to control apple scab, Venturia
inaequalis. One important part of the investigations was the application of different substances like
microbiological nutrient media, enzymes usually used for production of fruit juices and organic fertilizers
on their effect on the ascospore potential on depots of fallen leaves. Some substances like
TRYPTIC SOY BROTH increased the decomposition of the leaves significantly, other like BACTOFIL B
and HUMOFIX showed nearly no effect on the decomposition, but reduced the ascospore potential in
early spring by 80 % compared to the untreated control
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