836 research outputs found
Eigenmode in a misaligned triangular optical cavity
We derive relationships between various types of small misalignments on a
triangular Fabry-Perot cavity and associated geometrical eigenmode changes. We
focus on the changes of beam spot positions on cavity mirrors, the beam waist
position, and its angle. A comparison of analytical and numerical results shows
excellent agreement. The results are applicable to any triangular cavity close
to an isosceles triangle, with the lengths of two sides much bigger than the
other, consisting of a curved mirror and two flat mirrors yielding a waist
equally separated from the two flat mirrors. This cavity shape is most commonly
used in laser interferometry. The analysis presented here can easily be
extended to more generic cavity shapes. The geometrical analysis not only
serves as a method of checking a simulation result, but also gives an intuitive
and handy tool to visualize the eigenmode of a misaligned triangular cavity.Comment: 17 pages, 21 figure
Local Energy Gap in Deformed Carbon Nanotubes
The effects of graphite surface geometrical deformation on the dynamics of
conducting electrons are investigated theoretically. The analysis is performed
within the framework of a deformation-induced gauge field and corresponding
deformation-induced magnetic field. It is shown that the latter gives a local
energy gap along the axis of a deformed nanotube. We compare our energy gap
results with experimental data on energy gaps in nanotubes and peapods. We also
discuss the mixing of two Fermi points and construct a general model of low
energy dynamics, including a short-range deformation of the graphite sheet.
This model is equivalent to the Weyl equation in {\it U}(1) Abelian and {\it
SU}(2) non-Abelian deformation-induced gauge fields.Comment: 18 pages, 4 figures, corrected typos, added references, improved
presentation (v4, published version
First-principles study of phenyl ethylene oligomers as current-switch
We use a self-consistent method to study the distinct current-switch of
-amino-4-ethynylphenyl-4'-ethynylphenyl-5'-nitro-1-benzenethiol, from
the first-principles calculations. The numerical results are in accord with the
early experiment [Reed et al., Sci. Am. \textbf{282}, 86 (2000)]. To further
investigate the transport mechanism, we calculate the switching behavior of
p-terphenyl with the rotations of the middle ring as well. We also study the
effect of hydrogen atom substituting one ending sulfur atom on the transport
and find that the asymmetry of I-V curves appears and the switch effect still
lies in both the positive and negative bias range.Comment: 6 pages, 6 figure
Controlling edge states of zigzag carbon nanotubes by the Aharonov-Bohm flux
It has been known theoretically that localized states exist around zigzag
edges of a graphite ribbon and of a carbon nanotube, whose energy eigenvalues
are located between conduction and valence bands. We found that in metallic
single-walled zigzag carbon nanotubes two of the localized states become
critical, and that their localization length is sensitive to the mean curvature
of a tube and can be controlled by the Aharonov-Bohm flux. The curvature
induced mini-gap closes by the relatively weak magnetic field. Conductance
measurement in the presence of the Aharonov-Bohm flux can give information
about the curvature effect and the critical states.Comment: 5 pages, 4 figure
Aharonov-Bohm effect in higher genus materials
Flux periodicity of conducting electrons on a closed surface with genus two
(double torus) are investigated theoretically. We examine flux
periodicity of the ground-state energy and of the wave functions as a function
of applied magnetic field. A fundamental flux period of the ground-state energy
is twice a fundamental unit of magnetic flux for uniformly applied magnetic
field, which is shown to be valid for a simple ladder geometry and carbon
double torus. Flux periodicity of the wave functions in a double torus is
complicate as compared with a simple torus (), and an adiabatic addition
of magnetic fluxes does not provide a good quantum number for the energy
eigenstates. The results are extended to higher genus materials and the
implications of the results are discussed.Comment: 4 pages, 6 figure
Polarization Induced Switching Effect in Graphene Nanoribbon Edge-Defect Junction
With nonequilibrium Green's function approach combined with density
functional theory, we perform an ab initio calculation to investigate transport
properties of graphene nanoribbon junctions self-consistently. Tight-binding
approximation is applied to model the zigzag graphene nanoribbon (ZGNR)
electrodes, and its validity is confirmed by comparison with GAUSSIAN03 PBC
calculation of the same system. The origin of abnormal jump points usually
appearing in the transmission spectrum is explained with the detailed
tight-binding ZGNR band structure. Transport property of an edge defect ZGNR
junction is investigated, and the tunable tunneling current can be sensitively
controlled by transverse electric fields.Comment: 18 pages, 8 figure
- …