327 research outputs found
Optomechanical Kerker effect
Tunable directional scattering is of paramount importance for operation of
antennas, routing of light, and design of topologically protected optical
states. For visible light scattered on a nanoparticle the directionality could
be provided by the Kerker effect, exploiting the interference of electric and
magnetic dipole emission patterns. However, magnetic optical resonances in
small sub-100-nm particles are relativistically weak. Here, we predict
inelastic scattering with the unexpectedly strong tunable directivity up to
5.25 driven by a trembling of small particle without any magnetic resonance.
The proposed optomechanical Kerker effect originates from the vibration-induced
multipole conversion. We also put forward an optomechanical spin Hall effect,
the inelastic polarization-dependent directional scattering. Our results
uncover an intrinsically multipolar nature of the interaction between light and
mechanical motion. They apply to a variety of systems from cold atoms to
two-dimensional materials to superconducting qubits and can be instructive to
engineer chiral optomechanical coupling.Comment: 7 pages, 7 figures, 1 table + Method
Direct bandgap silicon quantum dots achieved via electronegative capping
We propose a novel concept of achieving silicon quantum dots with radiative
rates enhanced by more than two orders of magnitude up to the values
characteristic for direct band gap semiconductors. Our tight-binding
simulations show how the surface engineering can dramatically change the
density of confined electrons in real- and -space and give rise to the new
conduction band levels in -valley, thus promoting the direct radiative
transitions. The effect may be realized by covering the silicon dots with
covalently bonded electronegative ligands, such as alkyl or teflon chains
and/or by embedding in highly electronegative medium.Comment: 5 pages, 3 figures+ Supplementary Material
Optical transitions and energy relaxation of hot carriers in Si nanocrystals
Dynamics of hot carriers confined in Si nanocrystals is studied theoretically
using atomistic tight binding approach. Radiative, Auger-like and
phonon-assisted processes are considered. The Auger-like energy exchange
between electrons and holes is found to be the fastest process in the system.
However the energy relaxation of hot electron-hole pair is governed by the
single optical phonon emission. For a considerable number of states in small
nanocrystals single-phonon processes are ruled out by energy conservation law.Comment: 3 pages, 4 figure
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