476 research outputs found
Comment on "Impact of a Global Quadratic Potential on Galactic Rotation Curves"
Conformal gravity theory can explain observed flat rotation curves of
galaxies without invoking hypothetical dark matter. Within this theory, we
obtain a generic formula for the sizes of galaxies exploiting the stability
criterion of circular orbits. It is found that different galaxies have
different finite sizes uniquely caused by the assumed quadratic potential of
cosmological origin. Observations on where circular orbits might actually
terminate could thus be very instructive in relation to the galactic sizes
predicted here.Comment: 2 page
Complete absence of localization in a family of disordered lattices
We present analytically exact results to show that, certain quasi
one-dimensional lattices where the building blocks are arranged in a random
fashion, can have an absolutely continuous part in the energy spectrum when
special correlations are introduced among some of the parameters describing the
corresponding Hamiltonians. We explicitly work out two prototype cases, one
being a disordered array of a simple diamond network and isolated dots, and the
other an array of triangular plaquettes and dots. In the latter case, a
magnetic flux threading each plaquette plays a crucial role in converting the
energy spectrum into an absolutely continuous one. A flux controlled
enhancement in the electronic transport is an interesting observation in the
triangle-dot system that may be useful while considering prospective devices.
The analytical findings are comprehensively supported by extensive numerical
calculations of the density of states and transmission coefficient in each
case.Comment: 6 pages, 6 figures, epl draf
Magneto-transport in a mesoscopic ring with Rashba and Dresselhaus spin-orbit interactions
Electronic transport in a one-dimensional mesoscopic ring threaded by a
magnetic flux is studied in presence of Rashba and Dresselhaus spin-orbit
interactions. A completely analytical technique within a tight-binding
formalism unveils the spin-split bands in presence of the spin-orbit
interactions and leads to a method of determining the strength of the
Dresselhaus interaction. In addition to this, the persistent currents for
ordered and disordered rings have been investigated numerically. It is observed
that, the presence of the spin-orbit interaction, in general, leads to an
enhanced amplitude of the persistent current. Numerical results corroborate the
respective analytical findings.Comment: 7 pages, 7 figure
Metal-insulator transition in an aperiodic ladder network: an exact result
We show, in a completely analytical way, that a tight binding ladder network
composed of atomic sites with on-site potentials distributed according to the
quasiperiodic Aubry model can exhibit a metal-insulator transition at multiple
values of the Fermi energy. For specific values of the first and second
neighbor electron hopping, the result is obtained exactly. With a more general
model, we calculate the two-terminal conductance numerically. The numerical
results corroborate the analytical findings and yield a richer variety of
spectrum showing multiple mobility edges.Comment: 4 pages, 3 figure
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