643 research outputs found
Interlayer screening effect in graphene multilayers with ABA and ABC stacking
We study the effect of perpendicular electric fields on the band structures
of ABA and ABC graphene multilayers, and find that the electronic screening
effect is significantly different between them. In ABA multilayers, the field
produces a band overlap and gives a linear screening, while in ABC multilayers,
in contrast, it opens an energy gap in the surface-state band at low energy,
leading to a strong screening effect essentially non-linear to the field
amplitude. The energy gap of a large ABC stack sharply rises when the external
field exceeds a certain critical value.Comment: 8 pages, 6 figure
Integer quantum Hall effect and Hofstadter's butterfly spectra in three-dimensional metals in external periodic modulations
We propose that Hofstadter's butterfly accompanied by quantum Hall effect
that is similar to those predicted to occur in 3D tight-binding systems by
Koshino {\it et al.} [Phys. Rev. Lett. {\bf 86}, 1062 (2001)] can be realized
in an entirely different system -- 3D metals applied with weak external
periodic modulations (e.g., acoustic waves). Namely, an effect of two periodic
potentials interferes with Landau's quantization due to an applied magnetic
field \Vec{B}, resulting generally in fractal energy gaps as a function of
the tilting angle of \Vec{B}, for which the accompanying quantized Hall
tensors are computed. The phenomenon arises from the fact that, while the
present system has a different physical origin for the butterfly from the 3D
tight-binding systems, the mathematical forms are remarkably equivalent.Comment: 4 pages, 2 figure
Electronic structure of an electron on the gyroid surface, a helical labyrinth
Previously reported formulation for electrons on curved periodic surfaces is
used to analyze the band structure of an electron bound on the gyroid surface
(the only triply-periodic minimal surface that has screw axes). We find that an
effect of the helical structure appears as the bands multiply sticking together
on the Brillouin zone boundaries. We elaborate how the band sticking is lifted
when the helical and inversion symmetries of the structure are degraded. We
find from this that the symmetries give rise to prominent peaks in the density
of states.Comment: RevTeX, 4 pages, 6 figure
Duality and integer quantum Hall effect in isotropic 3D crystals
We show here a series of energy gaps as in Hofstadter's butterfly, which have
been shown to exist by Koshino et al [Phys. Rev. Lett. 86, 1062 (2001)] for
anisotropic three-dimensional (3D) periodic systems in magnetic fields
\Vec{B}, also arise in the isotropic case unless \Vec{B} points in
high-symmetry directions. Accompanying integer quantum Hall conductivities
can, surprisingly, take values
even for a fixed direction of \Vec{B}
unlike in the anisotropic case. We can intuitively explain the high-magnetic
field spectra and the 3D QHE in terms of quantum mechanical hopping by
introducing a ``duality'', which connects the 3D system in a strong \Vec{B}
with another problem in a weak magnetic field .Comment: 7 pages, 6 figure
Full Quantum Analysis of Two-Photon Absorption Using Two-Photon Wavefunction: Comparison with One-Photon Absorption
For dissipation-free photon-photon interaction at the single photon level, we
analyze one-photon transition and two-photon transition induced by photon pairs
in three-level atoms using two-photon wavefunctions. We show that the
two-photon absorption can be substantially enhanced by adjusting the time
correlation of photon pairs. We study two typical cases: Gaussian wavefunction
and rectangular wavefunction. In the latter, we find that under special
conditions one-photon transition is completely suppressed while the high
probability of two-photon transition is maintained.Comment: 6 pages, 4 figure
Orbital diamagnetism in multilayer graphenes: Systematic study with the effective mass approximation
We present a theoretical study on the orbital magnetism in multilayer
graphenes within the effective mass approximation. The Hamiltonian and thus
susceptibility can be decomposed into contributions from sub-systems equivalent
to monolayer or bilayer graphene. The monolayer-type subband exists only in odd
layers and exhibits a delta-function susceptibility at . The
bilayer-type subband appearing in every layer number gives a singular structure
in the vicinity of due to the trigonal warping as well as a logarithmic
tail away from . The integral of the susceptibility over energy is
approximately given only by the layer number.Comment: 12 pages, 5 figure
Electronic structure of periodic curved surfaces -- continuous surface versus graphitic sponge
We investigate the band structure of electrons bound on periodic curved
surfaces. We have formulated Schr\"{o}dinger's equation with the Weierstrass
representation when the surface is minimal, which is numerically solved. Bands
and the Bloch wavefunctions are basically determined by the way in which the
``pipes'' are connected into a network, where the Bonnet(conformal)-transformed
surfaces have related electronic strucutres. We then examine, as a realisation
of periodic surfaces, the tight-binding model for atomic networks
(``sponges''), where the low-energy spectrum coincides with those for
continuous curved surfaces.Comment: 4 page
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