2,178 research outputs found
Soft self-assembly of Weyl materials for light and sound
Soft materials can self-assemble into highly structured phases which
replicate at the mesoscopic scale the symmetry of atomic crystals. As such,
they offer an unparalleled platform to design mesostructured materials for
light and sound. Here, we present a bottom-up approach based on self-assembly
to engineer three-dimensional photonic and phononic crystals with topologically
protected Weyl points. In addition to angular and frequency selectivity of
their bulk optical response, Weyl materials are endowed with topological
surface states, which allows for the existence of one-way channels even in the
presence of time-reversal invariance. Using a combination of group-theoretical
methods and numerical simulations, we identify the general symmetry constraints
that a self-assembled structure has to satisfy in order to host Weyl points,
and describe how to achieve such constraints using a symmetry-driven pipeline
for self-assembled material design and discovery. We illustrate our general
approach using block copolymer self-assembly as a model system.Comment: published version, SI are available as ancillary files, code and data
are available on Zenodo at https://doi.org/10.5281/zenodo.1182581, PNAS
(2018
Photonic Localization of Interface Modes at the Boundary between Metal and Fibonacci Quasi-Periodic Structure
We investigated on the interface modes in a heterostructure consisting of a
semi-infinite metallic layer and a semi-infinite Fibonacci quasi-periodic
structure. Various properties of the interface modes, such as their spatial
localizations, self-similarities, and multifractal properties are studied. The
interface modes decay exponentially in different ways and the modes in the
lower stable gap possess highest spatial localization. A localization index is
introduced to understand the localization properties of the interface modes. We
found that the localization index of the interface modes in the upper stable
gap will converge to two slightly different constants according to the parity
of the Fibonacci generation. In addition, the localization-delocalization
transition is also found in the interface modes of the transient gap.Comment: 20 pages, 5figure
A Dirichlet-to-Neumann approach for the exact computation of guided modes in photonic crystal waveguides
This works deals with one dimensional infinite perturbation - namely line
defects - in periodic media. In optics, such defects are created to construct
an (open) waveguide that concentrates light. The existence and the computation
of the eigenmodes is a crucial issue. This is related to a self-adjoint
eigenvalue problem associated to a PDE in an unbounded domain (in the
directions orthogonal to the line defect), which makes both the analysis and
the computations more complex. Using a Dirichlet-to-Neumann (DtN) approach, we
show that this problem is equivalent to one set on a small neighborhood of the
defect. On contrary to existing methods, this one is exact but there is a price
to be paid : the reduction of the problem leads to a nonlinear eigenvalue
problem of a fixed point nature
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