6,779 research outputs found
Snake states in graphene quantum dots in the presence of a p-n junction
We investigate the magnetic interface states of graphene quantum dots that
contain p-n junctions. Within a tight-binding approach, we consider rectangular
quantum dots in the presence of a perpendicular magnetic field containing p-n,
as well as p-n-p and n-p-n junctions. The results show the interplay between
the edge states associated with the zigzag terminations of the sample and the
snake states that arise at the p-n junction, due to the overlap between
electron and hole states at the potential interface. Remarkable localized
states are found at the crossing of the p-n junction with the zigzag edge
having a dumb-bell shaped electron distribution. The results are presented as
function of the junction parameters and the applied magnetic flux.Comment: 13 pages, 23 figures, to be appeared in Phys. Rev.
Weakly holomorphic modular forms in prime power levels of genus zero
Let be the space of weight , level weakly holomorphic
modular forms with poles only at the cusp at . We explicitly construct
a canonical basis for for , and show that
many of the Fourier coefficients of the basis elements in are
divisible by high powers of the prime dividing the level . Additionally, we
show that these basis elements satisfy a Zagier duality property, and extend
Griffin's results on congruences in level 1 to levels 2, 3, 4, 5, 7, 8, 9, 16,
and 25
The split-operator technique for the study of spinorial wavepacket dynamics
The split-operator technique for wave packet propagation in quantum systems
is expanded here to the case of propagating wave functions describing
Schr\"odinger particles, namely, charge carriers in semiconductor
nanostructures within the effective mass approximation, in the presence of
Zeeman effect, as well as of Rashba and Dresselhaus spin-orbit interactions. We
also demonstrate that simple modifications to the expanded technique allow us
to calculate the time evolution of wave packets describing Dirac particles,
which are relevant for the study of transport properties in graphene.Comment: 19 pages, 4 figure
Gas expulsion in highly substructured embedded star clusters
We investigate the response of initially substructured, young, embedded star
clusters to instantaneous gas expulsion of their natal gas. We introduce
primordial substructure to the stars and the gas by simplistically modelling
the star formation process so as to obtain a variety of substructure
distributed within our modelled star forming regions. We show that, by
measuring the virial ratio of the stars alone (disregarding the gas
completely), we can estimate how much mass a star cluster will retain after gas
expulsion to within 10% accuracy, no matter how complex the background
structure of the gas is, and we present a simple analytical recipe describing
this behaviour. We show that the evolution of the star cluster while still
embedded in the natal gas, and the behavior of the gas before being expelled,
are crucial processes that affect the timescale on which the cluster can evolve
into a virialized spherical system. Embedded star clusters that have high
levels of substructure are subvirial for longer times, enabling them to survive
gas expulsion better than a virialized and spherical system. By using a more
realistic treatment for the background gas than our previous studies, we find
it very difficult to destroy the young clusters with instantaneous gas
expulsion. We conclude that gas removal may not be the main culprit for the
dissolution of young star clusters.Comment: 19 pages, 8 figures, 2 tables. Accepted for publication in MNRA
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