95 research outputs found
Statistics of resonance states in a weakly open chaotic cavity
In this letter, we demonstrate that a non-Hermitian Random Matrix description
can account for both spectral and spatial statistics of resonance states in a
weakly open chaotic wave system with continuously distributed losses. More
specifically, the statistics of resonance states in an open 2D chaotic
microwave cavity are investigated by solving the Maxwell equations with lossy
boundaries subject to Ohmic dissipation. We successfully compare the statistics
of its complex-valued resonance states and associated widths with analytical
predictions based on a non-Hermitian effective Hamiltonian model defined by a
finite number of fictitious open channels
Complete S-matrix in a microwave cavity at room temperature
We experimentally study the widths of resonances in a two-dimensional
microwave cavity at room temperature. By developing a model for the coupling
antennas, we are able to discriminate their contribution from those of ohmic
losses to the broadening of resonances. Concerning ohmic losses, we
experimentally put to evidence two mechanisms: damping along propagation and
absorption at the contour, the latter being responsible for variations of
widths from mode to mode due to its dependence on the spatial distribution of
the field at the contour. A theory, based on an S-matrix formalism, is given
for these variations. It is successfully validated through measurements of
several hundreds of resonances in a rectangular cavity.Comment: submitted to PR
Topological transition of Dirac points in a microwave experiment
By means of a microwave tight-binding analogue experiment of a graphene-like
lattice, we observe a topological transition between a phase with a point-like
band gap characteristic of massless Dirac fermions and a gapped phase. By
applying a controlled anisotropy on the structure, we investigate the
transition directly via density of states measurements. The wave function
associated with each eigenvalue is mapped and reveals new states at the Dirac
point, localized on the armchair edges. We find that with increasing
anisotropy, these new states are more and more localized at the edges.Comment: Physical Review Letters (2013) XX
Localized Modes in a Finite-Size Open Disordered Microwave Cavity
We present measurements of the spatial intensity distribution of localized
modes in a two-dimensional open microwave cavity randomly filled with
cylindrical dielectric scatterers. We show that each of these modes displays a
range of localization lengths and successfully relate the largest value to the
measured leakage rate at the boundary. These results constitute unambiguous
signatures of the existence of strongly localized electromagnetic modes in
two-dimensionnal open random media
Manipulation of edge states in microwave artificial graphene
Edge states are one important ingredient to understand transport properties
of graphene nanoribbons. We study experimentally the existence and the internal
structure of edge states under uniaxial strain of the three main edges: zigzag,
bearded, and armchair. The experiments are performed on artificial microwave
graphene flakes, where the wavefunctions are obtained by direct imaging. We
show that uniaxial strain can be used to manipulate the edge states: a single
parameter controls their existence and their spatial extension into the ribbon.
By combining tight-binding approach and topological arguments, we provide an
accurate description of our experimental findings. A new type of zero-energy
state appearing at the intersection of two edges, namely the corner state, is
also observed and discussed.Comment: 15 pages, 9 figure
Tight-binding couplings in microwave artificial graphene
We experimentally study the propagation of microwaves in an artificial
honeycomb lattice made of dielectric resonators. This evanescent propagation is
well described by a tight-binding model, very much like the propagation of
electrons in graphene. We measure the density of states, as well as the wave
function associated with each eigenfrequency. By changing the distance between
the resonators, it is possible to modulate the amplitude of
next-(next-)nearest-neighbor hopping parameters and to study their effect on
the density of states. The main effect is the density of states becoming
dissymmetric and a shift of the energy of the Dirac points. We study the basic
elements: An isolated resonator, a two-level system, and a square lattice. Our
observations are in good agreement with analytical solutions for corresponding
infinite lattice.Comment: 10 pages, 9 figure
Diffractive orbits in the length spectrum of a 2D microwave cavity with a small scatterer
In a 2D rectangular microwave cavity dressed with one point-like scatterer, a
semiclassical approach is used to analyze the spectrum in terms of periodic
orbits and diffractive orbits. We show, both numerically and experimentally,
how the latter can be accounted for in the so-called length spectrum which is
retrieved from 2-point correlations of a finite range frequency spectrum.
Beyond its fundamental interest, this first experimental evidence of the role
played by diffractive orbits in the spectrum of an actual cavity, can be the
first step towards a novel technique to detect and track small defects in wave
cavities.Comment: 14 pages, format IO
Boundary losses and spatial statistics of complex modes in a chaotic microwave cavity
submitted to PRLWe experimentally study the various manifestations of ohmic losses in a two-dimensional microwave chaotic cavity and exhibit two different contributions to the resonance widths. We show that the parts of these widths, which vary from mode to mode, are associated to ohmic losses located at the boundary of the cavity. We also describe how this non-proportional damping is responsible for the complex character of wavefunctions (corresponding to a spatially non-uniform phase), which is ubiquitous in open or dissipative wave systems. We experimentally demonstrate that the non-proportional widths are related to a single parameter, which measures the amount of complexity of wavefunctions, and provide theoretical arguments in favor of this relation
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