Sub-Terahertz Monochromatic Transduction with Semiconductor Acoustic Nanodevices

We demonstrate semiconductor superlattices or nanocavities as narrow band acoustic transducers in the sub-terahertz range. Using picosecond ultrasonics experiments in the transmission geometry with pump and probe incident on opposite sides of the thick substrate, phonon generation and detection processes are fully decoupled. Generating with the semiconductor device and probing on the metal, we show that both superlattices and nanocavities generate spectrally narrow wavepackets of coherent phonons with frequencies in the vicinity of the zone center and time durations in the nanosecond range, qualitatively different from picosecond broadband pulses usually involved in picosecond acoustics with metal generators. Generating in the metal and probing on the nanoacoustic device, we furthermore evidence that both nanostructured semiconductor devices may be used as very sensitive and spectrally selective detectors

Phonon Bloch oscillations in acoustic-cavity structures

We describe a semiconductor multilayer structure based in acoustic phonon cavities and achievable with MBE technology, designed to display acoustic phonon Bloch oscillations. We show that forward and backscattering Raman spectra give a direct measure of the created phononic Wannier-Stark ladder. We also discuss the use of femtosecond laser impulsions for the generation and direct probe of the induced phonon Bloch oscillations. We propose a gedanken experiment based in an integrated phonon source-structure-detector device, and we present calculations of pump and probe time dependent optical reflectivity that evidence temporal beatings in agreement with the Wannier-Stark ladder energy splitting.Comment: PDF file including 4 figure

Cavity polariton optomechanics: Polariton path to fully resonant dispersive coupling in optomechanical resonators

Resonant photoelastic coupling in semiconductor nanostructures opens new perspectives for strongly enhanced light-sound interaction in optomechanical resonators. One potential problem, however, is the reduction of the cavity Q-factor induced by dissipation when the resonance is approached. We show in this letter that cavity-polariton mediation in the light-matter process overcomes this limitation allowing for a strongly enhanced photon-phonon coupling without significant lifetime reduction in the strongly-coupled regime. Huge optomechanical coupling factors in the PetaHz/nm range are envisaged, three orders of magnitude larger than the backaction produced by the mechanical displacement of the cavity mirrors.Comment: 6 pages, 4 figure

Dispersion and damping of multi-quantum well polaritons from resonant Brillouin scattering by folded acoustic modes

We report on confined exciton resonances of acoustic and folded acoustic phonon light scattering in a GaAs/AlAs multi-quantum-well. Significant variations of the line shifts and widths are observed across the resonance and quantitatively reproduced in terms of the polariton dispersion. This high resolution Brillouin study brings new unexpectedly detailed informations on the polariton dynamics in confined systems

Electronic Raman scattering on under-doped Hg-1223 high-Tc superconductors:investigations on the symmetry of the order parameter

In order to obtain high quality, reliable electronic Raman spectra of a high-Tc superconductor compound, we have studied strongly under-doped HgBa2Ca2Cu3O8+d. This choice was made such as to i)minimize oxygen disorder in the Hg-plane generated by oxygen doping ii) avoid the need of phonon background subtraction from the raw data iii)eliminate traces of parasitic phases identified and monitored on the crystal surface. Under these experimental conditions we are able to present the pure electronic Raman response function in the B2g, B1g, A1g+B2g and A1g+B1g channels. The B2g spectrum exhibits a linear frequency dependence at low energy whereas the B1g one shows a cubic-like dependence. The B2g and B1g spectra display two well defined maxima at 5.6kBTc and 9kBTc respectively. In mixed A1g channels an intense electronic peak centered around 6.4 kBTc is observed. The low energy parts of the spectra correspond to the electronic response expected for a pure dx2-y2 gap symmetry and can be fitted up to the gap energy for the B1g channel. However, in the upper parts, the relative position of the B1g and B2g peaks needs expanding the B2g Raman vertex to second order Fermi surface harmonics to fit the data with the dx2-y2 model. The sharper and more intense A1g peak appears to challenge the Coulomb screening efficiency present for this channel. As compared to previous data on more optimally doped, less stoichiometric Hg-1223 compounds, this work reconciles the electronic Raman spectra of under- doped Hg-1223 crystals with the dx2-y2 model, provided that the oxygen doping is not too strong. This apparent extreme sensitivity of the electronic Raman spectra to the low lying excitations induced by oxygen doping in the superconducting state is emphasized here and remains an open question.Comment: 12 pages, 5 figure

Charge and spin density modulations in semiconductor quantum wires

We investigate static charge and spin density modulation patterns along a ferromagnet/semiconductor single junction quantum wire in the presence of spin-orbit coupling. Coherent scattering theory is used to calculate the charge and spin densities in the ballistic regime. The observed oscillatory behavior is explained in terms of the symmetry of the charge and spin distributions of eigenstates in the semiconductor quantum wire. Also, we discuss the condition that these charge and spin density oscillations can be observed experimentally.Comment: 7 pages, 8 figures (low-resolution

Tunable optical Aharonov-Bohm effect in a semiconductor quantum ring

By applying an electric field perpendicular to a semiconductor quantum ring we show that it is possible to modify the single particle wave function between quantum dot (QD)-like to ring-like. The constraints on the geometrical parameters of the quantum ring to realize such a transition are derived. With such a perpendicular electric field we are able to tune the Aharanov-Bohm (AB) effect for both single particles and for excitons. The tunability is in both the strength of the AB-effect as well as in its periodicity. We also investigate the strain induce potential inside the self assembled quantum ring and the effect of the strain on the AB effect

Collective excitation of quantum wires and effect of spin-orbit coupling in the presence of a magnetic field along the wire

The band structure of a quantum wire with the Rashba spin-orbit coupling develops a pseudogap in the presence of a magnetic field along the wire. In such a system spin mixing at the Fermi wavevectors $-k_F$ and $k_F$ can be different. We have investigated theoretically the collective mode of this system, and found that the velocity of this collective excitation depends sensitively on the strength of the Rashba spin-orbit interaction and magnetic field. Our result suggests that the strength of the spin-orbit interaction can be determined from the measurement of the velocity.Comment: RevTeX 4 file, 4pages, 6 eps figures. To appear in Physical Review

Strong Optical-Mechanical Coupling in a Vertical GaAs/AlAs Microcavity for Subterahertz Phonons and Near-Infrared Light

We show that distributed Bragg reflector GaAs/AlAs vertical cavities designed to confine photons are automatically optimal to confine phonons of the same wavelength, strongly enhancing their interaction. We study the impulsive generation of intense coherent and monochromatic acoustic phonons by following the time evolution of the elastic strain in picosecond-laser experiments. Efficient optical detection is assured by the strong phonon backaction on the high-Q optical cavity mode. Large optomechanical factors are reported (similar to THz/nm range). Pillar cavities based in these structures are predicted to display picogram effective masses, almost perfect sound extraction, and threshold powers for the stimulated emission of phonons in the range mu W-mW, opening the way for the demonstration of phonon "lasing" by parametric instability in these devices.Fil: Fainstein, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Comisión Nacional de Energía Atómica. Gerencia del Area de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Lanzillotti Kimura, N. D.. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Comisión Nacional de Energía Atómica. Gerencia del Area de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Jusserand, B.. Universite de Paris Vi. Institut Des Nanosciences de Paris; Francia. Centre National de la Recherche Scientifique; Francia. Universite Pierre et Marie Curie; FranciaFil: Perrin, B.. Universite de Paris Vi. Institut Des Nanosciences de Paris; Franci

Datta-Das transistor: Significance of channel direction, size-dependence of source contacts, and boundary effects

We analyze the spin expectation values for injected spin-polarized electrons (spin vectors) in a [001]-grown Rashba-Dresselhaus two-dimensional electron gas (2DEG). We generalize the calculation for point spin injection in semi-infinite 2DEGs to finite-size spin injection in bounded 2DEGs. Using the obtained spin vector formula, significance of the channel direction for the Datta-Das transistor is illustrated. Numerical results indicate that the influence due to the finite-size injection is moderate, while the channel boundary reflection may bring unexpected changes. Both effects are concluded to decrease when the spin-orbit coupling strength is strong. Hence [110] is a robust channel direction and is therefore the best candidate for the design of the Datta-Das transistor.Comment: 5 pages, 4 figures, accepted for publication in Physical Review