2,109 research outputs found
Coexistence of Localized and Extended States in Disordered Systems
It is commonly believed that Anderson localized states and extended states do
not coexist at the same energy. Here we propose a simple mechanism to achieve
the coexistence of localized and extended states in a band in a class of
disordered quasi-1D and quasi-2D systems. The systems are partially disordered
in a way that a band of extended states always exists, not affected by the
randomness, whereas the states in all other bands become localized. The
extended states can overlap with the localized states both in energy and in
space, achieving the aforementioned coexistence. We demonstrate such
coexistence in disordered multi-chain and multi-layer systems.Comment: 5 pages, 3 figure
Large Photonic Band Gaps in Certain Periodic and Quasi-Periodic Networks in two and three dimensions
The photonic band structures in certain two- and three-dimensional periodic
networks made of one-dimensional waveguides are studied by using the
Floquet-Bloch theorem. We find that photonic band gaps exist only in those
structures where the fundamental loop exhibits anti-resonant transmission. This
is also true for quasi-periodic networks in two and three dimensions, where the
photonic band structures are calculated from the spectra of total transmission
arising from a source inside the samples. In all the cases we have studied, it
is also found that the gap positions in a network are dictated by the
frequencies at which the anti-resonance occurs.Comment: 7 pages, 10 figures and 1 table. Published in Phys. Rev. B, 70,
125104 (2004
Illusion optics: The optical transformation of an object into another object
We propose to use transformation optics to generate a general illusion such
that an arbitrary object appears to be like some other object of our choice.
This is achieved by using a remote device that transforms the scattered light
outside a virtual boundary into that of the object chosen for the illusion,
regardless of the profile of the incident wave. This type of illusion device
also enables people to see through walls. Our work extends the concept of
cloaking as a special form of illusion to the wider realm of illusion optics.Comment: Including a paper and its auxiliary materia
Do Linear Dispersions of Classical Waves Mean Dirac Cones?
By using the \vec{k}\cdot\vec{p} method, we propose a first-principles theory
to study the linear dispersions in phononic and photonic crystals. The theory
reveals that only those linear dispersions created by doubly-degenerate states
can be described by a reduced Hamiltonian that can be mapped into the Dirac
Hamiltonian and possess a Berry phase of -\pi. Triply-degenerate states can
also generate Dirac-like cone dispersions, but the wavefunctions transform like
a spin-1 particle and the Berry phase is zero. Our theory is capable of
predicting accurately the linear slopes of Dirac/Dirac-like cones at various
symmetry points in a Brilliouin zone, independent of frequency and lattice
structure
Influence of microwave fields on the electron transport through a quantum dot in the presence of a direct tunneling between leads
We consider the time-dependent electron transport through a quantum dot
coupled to two leads in the presence of the additional over-dot (bridge)
tunneling channel. By using the evolution operator method together with the
wide-band limit approximation we derived the analytical formulaes for the
quantum dot charge and current flowing in the system. The influence of the
external microwave field on the time-average quantum dot charge, the current
and the derivatives of the average current with respect to the gate and
source-drain voltages has been investigated for a wide range of parameters.Comment: 28 Pages, 11 Postscript figure
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