Université de Fribourg

Fluctuations of the electromagnetic local density of states as a probe for structural phase switching

Sousa, N. de ; Sáenz, Juan José ; Scheffold, Frank ; García-Martín, A. ; Froufe-Pérez, Luis S.

In: Physical Review A, 2016, vol. 94, no. 4, p. 043832

We study the statistics of the fluorescence decay rates for single quantum emitters embedded in a scattering medium undergoing a phase transition. Under certain circumstances, the structural properties of the scattering medium explore a regime in which the system dynamically switches between two different phases. While in that regime the light-scattering properties of both phases are hardly...

Université de Fribourg

Role of short-range order and hyperuniformity in the formation of band gaps in disordered photonic materials

Froufe-Pérez, Luis S. ; Engel, Michael ; Damasceno, Pablo F. ; Muller, Nicolas ; Haberko, Jakub ; Glotzer, Sharon C. ; Scheffold, Frank

In: Physical Review Letters, 2016, vol. 117, no. 5, p. 053902

We study photonic band gap formation in two-dimensional high-refractive-index disordered materials where the dielectric structure is derived from packing disks in real and reciprocal space. Numerical calculations of the photonic density of states demonstrate the presence of a band gap for all polarizations in both cases. We find that the band gap width is controlled by the increase in...

Université de Fribourg

Magneto-Optical Activity in High Index Dielectric Nanoantennas

Sousa, N. de ; Froufe-Pérez, Luis S. ; Sáenz, Juan José ; García-Martín, A.

In: Scientific Reports, 2016, vol. 6, p. 30803

The magneto-optical activity, namely the polarization conversion capabilities of high- index, non-absorbing, core-shell dielectric nanospheres is theoretically analyzed. We show that, in analogy with their plasmonic counterparts, the polarization conversion in resonant dielectric particles is linked to the amount of electromagnetic field probing the magneto-optical material in the system....

Université de Fribourg

Self-diffusion and structural properties of confined fluids in dynamic coexistence

Sousa de, N. ; Sáenz, Juan José ; Scheffold, Frank ; García-Martín, A. ; Froufe-Pérez, Luis S.

In: Journal of Physics: Condensed Matter, 2016, vol. 28, no. 13, p. 135101

Self-diffusion and radial distribution functions are studied in a strongly confined Lennard-Jones fluid. Surprisingly, in the solid–liquid phase transition region, where the system exhibits dynamic coexistence, the self-diffusion constants are shown to present up to three-fold variations from solid to liquid phases at fixed temperature, while the radial distribution function corresponding...

Université de Fribourg

High-quality photonic crystals with a nearly complete band gap obtained by direct inversion of woodpile templates with titanium dioxide

Marichy, Catherine ; Muller, Nicolas ; Froufe-Pérez, Luis S. ; Scheffold, Frank

In: Scientific Reports, 2016, vol. 6, p. 21818

Photonic crystal materials are based on a periodic modulation of the dielectric constant on length scales comparable to the wavelength of light. These materials can exhibit photonic band gaps; frequency regions for which the propagation of electromagnetic radiation is forbidden due to the depletion of the density of states. In order to exhibit a full band gap, 3D PCs must present a threshold...

Université de Fribourg

Localized magnetic plasmons in all-dielectric $\ensuremath{\mu}<0$ metastructures

Paniagua-Domínguez, R. ; Froufe-Pérez, Luis S. ; Sáenz, J. J. ; Sánchez-Gil, J. A.

In: Physical Review B, 2015, vol. 91, no. 23, p. 235120

Metamaterials are known to exhibit a variety of electromagnetic properties nonexisting in nature. We show that an all-dielectric (nonmagnetic) system consisting of deep-subwavelength, high-permittivity resonant spheres possesses effective negative magnetic permeability (dielectric permittivity being positive and small). Due to the symmetry of the electromagnetic wave equations in classical...

Université de Fribourg

Controlling dispersion forces between small particles with artificially created random light fields

Brügger, Georges ; Froufe-Pérez, Luis S. ; Scheffold, Frank ; Sáenz, Juan José

In: Nature Communications, 2015, vol. 6, p. 7460

Appropriate combinations of laser beams can be used to trap and manipulate small particles with optical tweezers as well as to induce significant optical binding forces between particles. These interaction forces are usually strongly anisotropic depending on the interference landscape of the external fields. This is in contrast with the familiar isotropic, translationally invariant, van der Waals...

Université de Fribourg

Speckle fluctuations resolve the interdistance between incoherent point sources in complex media

Carminati, R. ; Cwilich, G. ; Froufe-Pérez, Luis S. ; Sáenz, J. J.

In: Physical Review A, 2015, vol. 91, no. 2, p. 023807

We study the fluctuations of the light emitted by two identical incoherent point sources in a disordered environment. The intensity-intensity correlation function and the speckle contrast, obtained after proper temporal and configurational averaging, encode the relative distance between the two sources. This suggests the intriguing possibility that intensity measurements at only one point in...

Université de Fribourg

Negative scattering asymmetry parameter for dipolar particles: Unusual reduction of the transport mean free path and radiation pressure

Gómez-Medina, R. ; Froufe-Pérez, Luis S. ; Yépez, M. ; Scheffold, Frank ; Nieto-Vesperinas, M. ; Sáenz, Juan José

In: Physical Review A - Atomic, molecular and optical physics, 2012, vol. 85, no. 3, p. 035802

Lossless dielectric nanospheres (made of nonmagnetic materials) with relatively low refraction index may present strong electric and magnetic dipolar resonances. We establish a relationship between the optical force from a plane wave on small electric and magnetic dipolar particles, the transport cross section, and the scattering asymmetry parameter g. In this way we predict negative g (that...

Université de Fribourg

Strong magnetic response of submicron Silicon particles in the infrared

García-Etxarri, A. ; Gómez-Medina, R. ; Froufe-Pérez, Luis S. ; López, C. ; Chantada, Laura ; Scheffold, Frank ; Aizpurua, J. ; Nieto-Vesperinas, M. ; Sáenz, Juan José

In: Optic Express, 2011, vol. 19, no. 6, p. 4815

High-permittivity dielectric particles with resonant magnetic properties are being explored as constitutive elements of new metamaterials and devices. Magnetic properties of low-loss dielectric nanoparticles in the visible or infrared are not expected due to intrinsic low refractive index of optical media in these regimes. Here we analyze the dipolar electric and magnetic response of lossless...