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Schmidt M.K.,Materials Physics Center EHU | Schmidt M.K.,Donostia International Physics Center | Aizpurua J.,Materials Physics Center EHU | Aizpurua J.,Donostia International Physics Center | And 5 more authors.
Physical Review Letters | Year: 2015

The polarization of the light scattered by an optically dense and random solution of dielectric nanoparticles shows peculiar properties when the scatterers exhibit strong electric and magnetic polarizabilities. While the distribution of the scattering intensity in these systems shows the typical irregular speckle patterns, the helicity of the incident light can be fully conserved when the electric and magnetic polarizabilities of the scatterers are equal. We show that the multiple scattering of helical beams by a random dispersion of "dual" dipolar nanospheres leads to a speckle pattern exhibiting a perfect isotropic constant polarization, a situation that could be useful in coherent control of light as well as in lasing in random media. © 2015 American Physical Society. Source


Schmidt M.K.,Materials Physics Center EHU | Schmidt M.K.,Donostia International Physics Center | Esteban R.,Donostia International Physics Center | Gonzalez-Tudela A.,Max Planck Institute of Quantum Optics | And 4 more authors.
ACS Nano | Year: 2016

Plasmon-enhanced Raman scattering can push single-molecule vibrational spectroscopy beyond a regime addressable by classical electrodynamics. We employ a quantum electrodynamics (QED) description of the coherent interaction of plasmons and molecular vibrations that reveal the emergence of nonlinearities in the inelastic response of the system. For realistic situations, we predict the onset of phonon-stimulated Raman scattering and a counterintuitive dependence of the anti-Stokes emission on the frequency of excitation. We further show that this QED framework opens a venue to analyze the correlations of photons emitted from a plasmonic cavity. © 2016 American Chemical Society. Source


Esteban R.,Materials Physics Center EHU | Esteban R.,Donostia International Physics Center | Zugarramurdi A.,CNRS Institute of Molecular Sciences | Zugarramurdi A.,Aalto University | And 9 more authors.
Faraday Discussions | Year: 2015

The optical response of plasmonic nanogaps is challenging to address when the separation between the two nanoparticles forming the gap is reduced to a few nanometers or even subnanometer distances. We have compared results of the plasmon response within different levels of approximation, and identified a classical local regime, a nonlocal regime and a quantum regime of interaction. For separations of a few Ångstroms, in the quantum regime, optical tunneling can occur, strongly modifying the optics of the nanogap. We have considered a classical effective model, so called Quantum Corrected Model (QCM), that has been introduced to correctly describe the main features of optical transport in plasmonic nanogaps. The basics of this model are explained in detail, and its implementation is extended to include nonlocal effects and address practical situations involving different materials and temperatures of operation. This journal is © The Royal Society of Chemistry. Source


Stradi D.,Autonomous University of Madrid | Stradi D.,IMDEA Madrid Institute for Advanced Studies | Barja S.,IMDEA Madrid Institute for Advanced Studies | Barja S.,Autonomous University of Madrid | And 17 more authors.
Physical Review Letters | Year: 2011

Elaborate density functional theory (DFT) calculations that include the effect of van der Waals (vdW) interactions have been carried out for graphene epitaxially grown on Ru(0001). The calculations predict a reduction of structural corrugation in the observed moiré pattern of about 25% (∼0.4Å) with respect to DFT calculations without vdW corrections. The simulated STM topographies are close to the experimental ones in a wide range of bias voltage around the Fermi level. © 2011 American Physical Society. Source


Stradi D.,Autonomous University of Madrid | Stradi D.,IMDEA Madrid Institute for Advanced Studies | Barja S.,IMDEA Madrid Institute for Advanced Studies | Barja S.,Autonomous University of Madrid | And 18 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

Monolayer graphene grown on Ru(0001) surfaces forms a superstructure with periodic modulations in its geometry and electronic structure. The large dimension and inhomogeneous features of this superstructure make its description and subsequent analysis a challenge for theoretical modeling based on density functional theory. In this work, we compare two different approaches to describe the same physical properties of this surface, focusing on the geometry and the electronic states confined at the surface. In the more complex approach, the actual moiré structure is taken into account by means of large unit cells, whereas in the simplest one, the graphene moiré is completely neglected by representing the system as a stretched graphene layer that adapts pseudomorphically to Ru(0001). As shown in previous work, the more complex model provides an accurate description of the existing experimental observations. More interestingly, we show that the simplified stretched models, which are computationally inexpensive, reproduce qualitatively the main features of the surface electronic structure. They also provide a simple and comprehensive picture of the observed electronic structure, thus making them particularly useful for the analysis of these and maybe other complex interfaces. © 2013 American Physical Society. Source

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