1,838 research outputs found
Non-Hamiltonian dynamics in optical microcavities resulting from wave-inspired corrections to geometric optics
We introduce and investigate billiard systems with an adjusted ray dynamics
that accounts for modifications of the conventional reflection of rays due to
universal wave effects. We show that even small modifications of the specular
reflection law have dramatic consequences on the phase space of classical
billiards. These include the creation of regions of non-Hamiltonian dynamics,
the breakdown of symmetries, and changes in the stability and morphology of
periodic orbits. Focusing on optical microcavities, we show that our adjusted
dynamics provides the missing ray counterpart to previously observed wave
phenomena and we describe how to observe its signatures in experiments. Our
findings also apply to acoustic and ultrasound waves and are important in all
situations where wavelengths are comparable to system sizes, an increasingly
likely situation considering the systematic reduction of the size of electronic
and photonic devices.Comment: 6 pages, 4 figures, final published versio
Boundary-induced violation of the Dirac fermion parity and its signatures in local and global tunneling spectra of graphene
Extended defects in graphene, such as linear edges, break the translational
invariance and can also have an impact on the symmetries specific to massless
Dirac-like quasiparticles in this material. The paper examines the consequences
of a broken Dirac fermion parity in the framework of the effective boundary
conditions varying from the Berry-Mondragon mass confinement to a zigzag edge.
The parity breaking reflects the structural sublattice asymmetry of zigzag-type
edges and is closely related to the previously predicted time-reversal
symmetric edge states. We calculate the local and global densities of the edge
states and show that they carry a specific polarization, resembling, to some
extent, that of spin-polarized materials. The lack of the parity leads to a
nonanalytical particle-hole asymmetry in the edge-state properties. We use our
findings to interpret recently observed tunneling spectra in zigzag-terminated
graphene. We also propose a graphene-based tunneling device where the
particle-hole asymmetric edge states result in a strongly nonlinear
conductance-voltage characteristics, which could be used to manipulate the
tunneling transport.Comment: 8 pages, 5 figures, to be published in Phys. Rev.
Orthogonality catastrophe and Kondo effect in graphene
Anderson's orthogonality catastrophe in graphene, at energies close to the
Dirac point, is analyzed. It is shown that, in clean systems, the orthogonality
catastrophe is suppressed, due to the vanishing density of states at the Dirac
point. In the presence of preexisting localized states at the Dirac energy, the
orthogonality catastrophe shows similar features to those found in normal
metals with a finite density of states at the Fermi level. The implications for
the Kondo effect induced by magnetic impurities, and for the Fermi edge
singularities in tunneling processes are also discussed.Comment: 7 pages, 7 figure
Asymmetric scattering and non-orthogonal mode patterns in optical micro-spirals
Quasi-bound states in an open system do in general not form an orthogonal and
complete basis. It is, however, expected that the non-orthogonality is weak in
the case of well-confined states except close to a so-called exceptional point
in parameter space. We present numerical evidence showing that for passive
optical microspiral cavities the parameter regime where the non-orthogonality
is significant is rather broad. Here we observe almost-degenerate pairs of
well-confined modes which are highly non-orthogonal. Using a non-Hermitian
model Hamiltonian we demonstrate that this interesting phenomenon is related to
the asymmetric scattering between clockwise and counterclockwise propagating
waves in the spiral geometry. Numerical simulations of ray dynamics reveal a
clear ray-wave correspondence.Comment: 8 pages, 10 figure
Non-Universality of the Specific Heat in Glass Forming Systems
We present new simulation results for the specific heat in a classical model
of a binary mixture glass-former in two dimensions. We show that in addition to
the formerly observed specific heat peak there is a second peak at lower
temperatures which was not observable in earlier simulations. This is a
surprise, as most texts on the glass transition expect a single specific heat
peak. We explain the physics of the two specific heat peaks by the
micro-melting of two types of clusters. While this physics is easily
accessible, the consequences are that one should not expect any universality in
the temperature dependence of the specific heat in glass formers
Do Athermal Amorphous Solids Exist?
We study the elastic theory of amorphous solids made of particles with finite
range interactions in the thermodynamic limit. For the elastic theory to exist
one requires all the elastic coefficients, linear and nonlinear, to attain a
finite thermodynamic limit. We show that for such systems the existence of
non-affine mechanical responses results in anomalous fluctuations of all the
nonlinear coefficients of the elastic theory. While the shear modulus exists,
the first nonlinear coefficient B_2 has anomalous fluctuations and the second
nonlinear coefficient B_3 and all the higher order coefficients (which are
non-zero by symmetry) diverge in the thermodynamic limit. These results put a
question mark on the existence of elasticity (or solidity) of amorphous solids
at finite strains, even at zero temperature. We discuss the physical meaning of
these results and propose that in these systems elasticity can never be
decoupled from plasticity: the nonlinear response must be very substantially
plastic.Comment: 11 pages, 11 figure
An Efficient Algorithm for Optimizing Adaptive Quantum Metrology Processes
Quantum-enhanced metrology infers an unknown quantity with accuracy beyond
the standard quantum limit (SQL). Feedback-based metrological techniques are
promising for beating the SQL but devising the feedback procedures is difficult
and inefficient. Here we introduce an efficient self-learning
swarm-intelligence algorithm for devising feedback-based quantum metrological
procedures. Our algorithm can be trained with simulated or real-world trials
and accommodates experimental imperfections, losses, and decoherence
Sounds Like a Fit! Wording in Recruitment Advertisements and Recruiter Gender Affect Women’s Pursuit of Career Development Programs via Anticipated Belongingness
Following calls for research to increase gender equality, we investigated women's intentions to pursue career opportunities, in the form of career development programs. We built on lack of fit and signaling theory to argue that women's but not men's pursuit of career opportunities would be influenced by recruiter gender and gender‐stereotypical wording in recruitment advertisements. We conducted two studies in Germany. In Study 1 (video‐based experiment with 329 university students), we found that when a male recruiter used stereotypically masculine compared to feminine wording, female students anticipated lower belongingness, expected lower success of an application, and indicated lower application intentions for career opportunities. These differences in female students’ evaluations disappeared when the recruiter was female. While Study 2 (experimental vignette study with 545 employees) replicates the negative effects of masculine wording for female employees; the buffering effect of female recruiters was only replicated for younger, but not for older female employees. Women's anticipated belongingness mediated the relationship between advertisement wording and application intentions when the recruiter was male. Recruiter gender and wording had no effects on men. Our work contributes to a better understanding of when and why contextual characteristics in the recruitment process influence women's pursuit of career opportunities
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