Rair Macêdo

Spin canting induced nonreciprocal Goos-Hänchen shifts

Recent studies on surface reflection illustrate how light beams can be laterally shifted from the position predicted by geometrical optics, the so called Goos-Hänchen effect. In antiferromagnets this shifts can be controlled with an external magnetic field. We show that a configuration in which spins cant in response to applied magnetic fields enhance possibilities of field controlled shifts. Moreover, we show that nonreciprocal displacements are possible, for both oblique and normal incidence, due to inherent nonreciprocity of the polariton phase with respect to the propagation direction. In the absence of an external field, reciprocal displacements occur.

Far Infrared Slab Lensing and Subwavelength Imaging in Crystal Quartz

Departamento de F´isica, Universidade Federal do Ceara´, Campus Pici, 60455-900 Fortaleza CE, Brazil(Dated: November 20, 2012)We examine the possibility of using negative refraction stemming from the phonon polaritonresponse in an anisotropic crystal to create a simple slab lens with plane parallel sides, and show thatimaging from such a lens should be possible at room temperature despite the effects of absorptionthat are inevitably present due to phonon damping. In particular, we consider the case of crystalquartz, a system for which experimental measurements consistent with all-angle negative refractionassociated with the phonon polariton response have already been demonstrated. Furthermore, weinvestigate the possibility of subwavelength imaging from such materials, and show that it shouldbe possible for certain configurations.

Beam shifts on reflection of electromagnetic radiation off anisotropic crystals at optic phonon frequencies

We discuss possible beam shifts on external reflection of electromagnetic radiation off an anisotropic crystal around its optic phonon frequencies. In certain situations, these displacements may oppose the energy flow within the crystal. We show examples for reflection off crystal quartz in various configurations. Displacements of the order of a wavelength should occur with significant reflected intensity.

Electric and magnetic field effects on the excitonic properties of elliptic core–multishell quantum wires

The effect of eccentricity distortions of core-multishell quantum wires on their electron, hole and exciton states is theoretically investigated. Within the effective mass approximation, the Schrödinger equation is numerically solved for electrons and holes in systems with single and double radial heterostructures, and the exciton binding energy is calculated by means of a variational approach. We show that the energy spectrum of a core-multishell heterostructure with eccentricity distortions, as well as its magnetic field dependence, are very sensitive to the direction of an externally applied electric field, an effect that can be used to identify the eccentricity of the system. For a double heterostructure, the eccentricities of the inner and outer shells play an important role on the excitonic binding energy, especially in the presence of external magnetic fields, and lead to drastic modifications in the oscillator strength.

Using magnetic hyperbolic metamaterials as high frequency tunable filters

Metamaterials have enabled a series of major advances in optical devices in the past decade. Here, we suggest a type of hyperbolic metamaterial based on spin canting in magnetic multi-layers. We show that these structures have unique features in microwave waveguides that act as tunable filters. In the resulting band pass filter, we demonstrate an exceptional frequency tunability of 30 GHz with external fields smaller than 500 Oe. Unlike single metallic ferromagnetic films, we also demonstrate a high-frequency band-stop filter at very low fields.

Magnetic field induced shell-to-core confinement transition in type-II semiconductor quantum wires

We investigate the excitonic properties of a core-multishell semiconductor nanowire with type-II band mismatch, i.e., with spatially separated electrons and holes, under an external magnetic field. Our results demonstrate that, depending on the core wire radius, the carrier in the type-II band exhibits either a quantum dot-like or a quantum ring-like energy spectrum, corresponding to a carrier confinement in the core wire or in the outer shell, respectively. In the latter, a shell-to-core confinement transition can be induced by increasing the magnetic field intensity, which may lead to interesting photocurrent properties of these confining structures, tunable by the external field.

Beam shifts of Far-Infrared Radiation on Reflection off the Anisotropic Crystal LiYF 4

We investigate the Goos-Hanchen shifts associated with phonons in the anisotropic crystal LiYF4. In p-polarization the shifts can be either positive or negative, and various mechanism are discussed.

The role of surface roughness on the electron confinement in semiconductor quantum dots

Using the effective mass approximation, we present a theoretical study of surface roughness effects on electron energies in semiconductor quantum dots, which are demonstrated to increase up to approximately 6%