24,269 research outputs found
HST/FOS Eclipse mapping of IP Pegasi in outburst
We report the results of a time-resolved eclipse mapping of the dwarf nova IP
Pegasi during the decline of its May 1993 outburst from HST/FOS fast
spectroscopy covering 3 eclipses in the ultraviolet spectral range.Comment: 1 page 0 figure
Pseudospin and Deformation-induced Gauge Field in Graphene
The basic properties of -electrons near the Fermi level in graphene are
reviewed from a point of view of the pseudospin and a gauge field coupling to
the pseudospin. The applications of the gauge field to the electron-phonon
interaction and to the edge states are reported.Comment: 27 pages, 7 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
Aharanov-Bohm effect for the edge states of zigzag carbon nanotubes
Two delocalized states of metallic zigzag carbon nanotubes near the Dirac
point can be localized by the Aharanov-Bohm magnetic field around 20 Tesla. The
dependence of the localization on the length and diameter of the nanotubes
shows that the localization-delocalization transition can be observed for 2 nm
diameter tube. The mechanism of the localization is explained in terms of the
deformation-induced gauge field, which shows a topological nature of the
localization. The transition from the delocalized states to the localized
states can be observed by scanning tunneling microscopy and spectroscopy. A
similarity between the transition and the spin Hall effect is discussed.Comment: 7 pages, 4 figure
Stabilization mechanism of edge states in graphene
It has been known that edge states of a graphite ribbon are zero-energy,
localized eigen-states. We show that next nearest-neighbor hopping process
decreases the energy of the edge states at zigzag edge with respect to the
Fermi energy. The energy reduction of the edge states is calculated
analytically by first-order perturbation theory and numerically. The resultant
model is consistent with the peak of recent scanning tunneling spectroscopy
measurements.Comment: 4 pages, 2 figures, final version to appear in Applied Physics
Letter
Fractional Flux Periodicity in Doped Carbon Nanotubes
An anomalous magnetic flux periodicity of the ground state is predicted in
two-dimensional cylindrical surface composed of square and honeycomb lattice.
The ground state and persistent currents exhibit an approximate fractional
period of the flux quantum for a specific Fermi energy. The period depends on
the aspect ratio of the cylinder and on the lattice structure around the axis.
We discuss possibility of this nontrivial periodicity in a heavily doped
armchair carbon nanotube.Comment: 5 pages, 4 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
Intersecting D-brane states derived from the KP theory
A general scheme to find tachyon boundary states is developed within the
framework of the theory of KP hierarchy. The method is applied to calculate
correlation function of intersecting D-branes and rederived the results of our
previous works as special examples. A matrix generalization of this scheme
provides a method to study dynamics of coincident multi D-branes.Comment: 10 page
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