Showing papers by "Paulo V. Santos published in 2006"
TL;DR: In this article, a compact optical waveguide modulator based on a Mach-Zehnder interferometer driven by surface acoustic waves was demonstrated, achieving peak-to-peak modulation exceeding 90% of the average transmission and operation in the gigahertz frequency range.
Abstract: The authors demonstrate a compact optical waveguide modulator based on a Mach-Zehnder interferometer driven by surface acoustic waves. The modulator was monolithically fabricated on GaAs with an active region length of approximately 15μm. It yields peak-to-peak modulation exceeding 90% of the average transmission and operation in the gigahertz frequency range.
82 citations
TL;DR: It is shown that the coherent interaction between microcavity polaritons and externally stimulated acoustic phonons forms a tunable polariton superlattice with a folded energy dispersion determined by the phonon population and wavelength.
Abstract: We show that the coherent interaction between microcavity polaritons and externally stimulated acoustic phonons forms a tunable polariton superlattice with a folded energy dispersion determined by the phonon population and wavelength. Under high phonon concentration, the strong confinement of the optical and excitonic polariton components in the phonon potential creates weakly coupled polariton wires with a virtually flat energy dispersion.
66 citations
TL;DR: In this article, the influence of surface acoustic waves (SAWs) on the magnetization of a Mn12-acetate single crystal was reported on the surface of a piezoelectric LiNbO3 substrate containing an interdigital transducer for the excitation of SAWs.
Abstract: We report here on the influence of surface acoustic waves (SAWs) on the magnetization of a Mn12-acetate single crystal The crystal was mounted on the surface of a piezoelectric LiNbO3 substrate containing an interdigital transducer for the excitation of SAWs The magnetization of the crystal was measured using a rf superconducting quantum interference device with a time resolution of 1μs The piezoelectric material was excited by SAW pulses of different frequencies produced by applying microwave pulses to the transducer Our data show that molecular magnets onto the LiNbO3 surface can be used as very sensitive detectors of the SAW frequency and intensity
16 citations
TL;DR: In this article, the spin-splitting parameter for a GaAs quantum well was determined to be 7 = 17 ± 2 eV A 3 as well as the effects of the SAW strain field on the spin dynamics.
Abstract: Mobile quantum dots (denoted as dynamic quantum dots) formed by the interference of orthogonal beams of surface acoustic waves (SAWs) in an undoped GaAs quantum well coherently transport electron spins over distances exceeding 70 μm. We determine the spin-splitting parameter for a GaAs quantum well to be 7 = 17 ± 2 eV A 3 as well as investigate the effects of the SAW strain field on the spin dynamics.
11 citations
TL;DR: In this article, a well consisting of (In,Ga)As/GaAs and InAs/GAAs was grown on GaAs(110) by conventional molecular beam epitaxy as well as by migration enhanced epitaxy and studied by low-temperature photoluminescence, atomic force microscopy and transmission electron microscopy.
Abstract: Quantum wells consisting of (In,Ga)As/GaAs and InAs/GaAs were grown on GaAs(110) by conventional molecular beam epitaxy as well as by migration enhanced epitaxy and studied by low-temperature photoluminescence, atomic force microscopy and transmission electron microscopy. Increasing the In mole fraction or the well thickness degrades the structural perfection more dramatically in (110)-oriented structures than in (001)-oriented ones while post-growth annealing improves the optical properties. The quality of (In,Ga)As wells is remarkably improved by migration enhanced epitaxy. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
7 citations
TL;DR: In this paper, the temperature dependence of the coherence length of electron spins during transport was investigated using spatially resolved photoluminescence, and it was shown that at temperatures between 4.2 and 20.2 K, the spin coherence remained constant at approximately 100 μ m.
Abstract: Electron spins in an undoped quantum well are transported using dynamic quantum dots (DQDs) formed by the piezoelectric potential of surface acoustic waves. The temperature dependence of the coherence length of electron spins during transport is investigated using spatially resolved photoluminescence. For temperatures between 4.2 and 20 K, the spin coherence length, which is proportional to the spin coherence lifetime, remains constant at approximately 100 μ m. This results from the ability of the DQDs to confine the spins within a small area (1 μ m × 1 μ m to 2 μ m × 2 μ m) during transport and reduce the temperature dependence associated with D’yakonov-Perel’ (DP) spin scattering. At 30 K, the electron spin coherence length rapidly decreases as the DP mechanism becomes dominant because of the higher thermal velocity on the Fermi surface.
4 citations
TL;DR: In this article, the authors investigated the dynamics of radiative trapping centers during the ambipolar transport of electrons and holes induced by acoustic fields and proposed a model for electron trapping based on the injection of carriers induced by the surface acoustic wave piezoelectric field into states at the interface between the GaAs quantum well and the (Al,Ga)As barriers.
Abstract: We investigate the dynamics of radiative trapping centers during the ambipolar transport of electrons and holes induced by acoustic fields. The studies used spatially resolved photoluminescence spectroscopy to determine the nature of the trapping centers for different transport conditions. For low and moderate acoustic powers, the primary traps are electron capturing centers while hole trapping becomes important for high acoustic powers. A remarkable feature of these radiative trapping centers is that their capture cross section depends on the acoustic power. We propose a model for electron trapping based on the injection of carriers induced by the surface acoustic wave piezoelectric field into states at the interface between the GaAs quantum well and the (Al,Ga)As barriers.
4 citations
TL;DR: In this paper, the authors review processes for long-range spin transport and manipulation in GaAs quantum wells using mobile potentials created by the piezoelectric field of a surface acoustic wave.
Abstract: We review processes for long-range spin transport and manipulation in GaAs quantum wells using mobile potentials created by the piezoelectric field of a surface acoustic wave. By reducing spin dephasing mechanisms associated with the spin orbit-coupling, these potentials can coherently transport spins over distances on the order of 100 µm. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
3 citations
TL;DR: The interaction between surface acoustic waves (SAWs) with (Al,Ga)As microcavity polaritons results in the formation of a dynamic optical superlattice with folded light dispersion and energy stop bands when the lower polariton branch is predominantly of photonic character.
Abstract: The interaction between surface acoustic waves (SAWs) with (Al,Ga)As microcavity polaritons results in the formation of a dynamic optical superlattice with folded light dispersion and energy stop bands when the lower polariton branch is predominantly of photonic character. For small detunings between the excitonic and optical cavity resonances, the SAW bleaches the polariton resonances through the efficient dissociation of the excitons by its piezoelectric field.
TL;DR: The geometry of the sample is shown to dictate the importance of strain on the spin-orbit splitting of the conduction band for electrons transported via dynamic quantum dots (DQDs) generated by surface acoustic waves (SAWs) as discussed by the authors.
Abstract: The geometry of the sample is shown to dictate the importance of strain on the spin-orbit splitting of the conduction band for electrons transported via dynamic quantum dots (DQDs) generated by surface acoustic waves (SAWs). Photoluminescence measurements monitoring the Larmor precession of electron spins in the absence of an applied magnetic field are used to characterize the spin-orbit splitting of the conduction band. We show that, in thick quantum wells (QWs), the Dresselhaus spin-orbit contribution to the precession frequency reduces and may become comparable to the one associated with the strain field induced by the SAW. We attribute deviations in the measured precession frequency to strain effects, which become more pronounced for QWs located closer to the surface because of the larger SAW strain field. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
21 May 2006
TL;DR: In this paper, a mini-Brillouin zone and band folding of the polariton dispersion were demonstrated for the first time using surface acoustic waves, and the results were in good agreement with model calculations.
Abstract: We modulate cavity-polaritons using surface acoustic waves. The corresponding formation of a mini-Brillouin zone and band folding of the polariton dispersion is demonstrated for the first time. Results are in good agreement with model calculations.