13,561 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
Stacking Order dependent Electric Field tuning of the Band Gap in Graphene Multilayers
The effect of different stacking order of graphene multilayers on the
electric field induced band gap is investigated. We considered a positively
charged top and a negatively charged back gate in order to independently tune
the band gap and the Fermi energy of three and four layer graphene systems. A
tight-binding approach within a self-consistent Hartree approximation is used
to calculate the induced charges on the different graphene layers. We found
that the gap for trilayer graphene with the ABC stacking is much larger than
the corresponding gap for the ABA trilayer. Also we predict that for four
layers of graphene the energy gap strongly depends on the choice of stacking,
and we found that the gap for the different types of stacking is much larger as
compared to the case of Bernal stacking. Trigonal warping changes the size of
the induced electronic gap by approximately 30% for intermediate and large
values of the induced electron density
Explaining the wage gap: Heckscher-Ohlin, economic geography and services availability
In the debate on globalisation and wage inequality Heckscher-Ohlin, economic geography and services availability theory has featured prominently. However, a neglected mechanism by which globalisation affects labour market outcomes is through the in-creased tradability of producer services. By integrating elements of Heck-scher- Ohlin theory, the economic geography literature and the literature on producer services linkages, we show that the impact of globalisation on the relative wages is a sophisticated combination of the effects that play a key-role in these models. The most important result we find is that the fall in transportation costs of producer services might indeed have caused the sharp increase in wage inequality. (JEL F1, R1)
Carbon clusters: From ring structures to nanographene
The lowest energy configurations of Cn(n =< 55) clusters are obtained using
the energy mini- mization technique with the conjugate gradient (CG) method
where a modified Brenner potential is invoked to describe the carbon and
hydrocarbon interaction. We found that the ground state configuration consists
of a single ring for small number of C atoms and multi-ring structures are
found with increasing n, which can be in planar, bowl-like or cap-like form.
Contrary to previous predictions, the binding energy Eb does not show even-odd
oscillations and only small jumps are found in the Eb(n) curve as a consequence
of specific types of edges or equivalently the number of secondary atoms. We
found that hydrogenation of the edge atoms may change the ground state
configuration of the nanocluster. In both cases we determined the magic
clusters. Special attention is paid to trigonal and hexagonal shaped carbon
clusters and to clusters having a graphene-like configuration. Trigonal
clusters are never the ground state, while hexagonal shaped clusters are only
the ground state when they have zigzag edges.Comment: Accepted for publication in Phys. Rev.
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