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 $k$-space and give rise to the new conduction band levels in $\Gamma$-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