arXiv subjects

E. R. Cardozo de Oliveira

Publications and source records attributed to E. R. Cardozo de Oliveira.

10 recordsLinked to original sources

arXiv2026

GaAs/AlAs Acoustic Nanocavities for Coherent GHz-THz Phonon Engineering

The controlled confinement of high-frequency acoustic phonons in semiconductor nanostructures has emerged as a key ingredient for functional nanophononic and hybrid quantum technologies. In this Review, we summarize recent advances that have established GaAs/AlAs acoustic nanocavities as a versatile and scalable platform for GHz-THz phonon engineering. Compared with alternative nanophononic platforms, GaAs/AlAs offers a particularly favorable combination of mature epitaxial growth, strong photoelastic coupling, and simultaneous optical-acoustic mode colocalization across the GHz-THz regime. We focus on distributed Bragg reflector (DBR)-based architectures, with particular emphasis on micropillar resonators enabling three-dimensional phonon confinement and strong colocalization of acoustic and optical fields. Recent developments in ultrafast optical techniques, including picosecond ultrasonics and Brillouin scattering, have provided unprecedented access to phonon dynamics, coherence, and dissipation at the nanoscale. These advances, combined with strong optophononic coupling, have enabled efficient coherent generation, detection, and manipulation of confined acoustic modes. We discuss key performance metrics, integration strategies, and remaining challenges, notably in acousto-optic transduction efficiency and scalable electrical control. Finally, we outline near-term perspectives for nonlinear phononics, hybrid quantum systems, and integrated phononic circuits, positioning GaAs/AlAs heterostructures as a robust and scalable platform for next-generation nanophononic functionalities.

cond-mat.mes-hall↗

arXiv2026

Coupled Topological Interface States and Phonon Molecules in GaAs/AlAs Superlattices

Topological interface states in one-dimensional superlattices provide spatially localized phonon modes protected by the topology of the underlying band structure. In GaAs/AlAs distributed Bragg reflectors (DBRs), such states can be engineered through band inversion between superlattices with opposite Zak phases within the Su-Schrieffer-Heeger (SSH) framework. Here, we demonstrate topological phonon molecules and extended chains formed by coupled nanophononic interface states. By concatenating three superlattices with alternating topology, we realize two coupled interface states that hybridize into symmetric and antisymmetric modes, whose splitting can be tuned over tens of gigahertz by varying the reflectivity of the central DBR. Extending this concept, we engineer chains of up to N=6 coupled interface states that form narrow topological minibands while remaining strongly localized at the interfaces. We experimentally observe these coupled states in molecular-beam-epitaxy-grown GaAs/AlAs heterostructures using time-domain pump-probe transient reflectivity measurements, and reproduce their behavior using transfer-matrix calculations and a simple analytical model for the mode splitting. These results establish topological interface states as a robust platform for engineering coupled phononic systems and tunable nanophononic architectures in the GHz regime.

cond-mat.mes-hall↗

arXiv2025

Structural, magnetic, and nanoacoustic characterization of Co/Pt superlattices

Superlattices presenting a spatial modulation of the elastic properties appear as a main tool to reach the THz regime in nanoacoustic devices. The exploration of alternative materials with multifunctional properties remains a fertile domain of research. In this work, we study the structural, magnetic, and acoustic characteristics of nanometric superlattices made of Pt/Co. The samples present a well defined periodicity, as determined by X-ray reflectometry, whereas scanning transmission electron microscopy with local compositional analysis reveals that the superlattices present a modulation in composition instead of sharp interfaces. The policrystalline nature of the superlattices is evidenced both by X ray diffraction and transmission electron microscopy. Magnetization measurements show a perpendicular magnetic anisotropy for the higher Co concentrations. Picosecond acoustic experiments evidence that the studied samples support short-lived acoustic modes up to 900 GHz, and up to 7 acoustic echoes at lower frequencies.These are promising results for the development of magnetoacoustic devices working at ultrahigh frequencies.

cond-mat.mtrl-sci↗

arXiv2024

Interference of ultrahigh frequency acoustic phonons from distant quasi-continuous sources

The generation of propagating acoustic waves is essential for telecommunication applications, quantum technologies, and sensing. Up to now, the electrical generation has been at the core of most implementations, but is technologically limited to a few gigahertz. Overcoming this frequency limit holds the prospect of faster modulators, quantum acoustics at higher working temperatures, nanoacoustic sensing from smaller volumes. Alternatively, the optical excitation of acoustic resonators has unlocked frequencies up to 1 THz, but in most cases, the acoustic energy cannot be efficiently extracted from the resonator into a propagating wave. Here, we demonstrate a quasi-continuous and coherent source of 20 GHz acoustic phonons, based on a ridge waveguide, structured in the vertical direction as a high-Q acousto-optic resonator. The high frequency phonons propagate up to 20 $μ$m away from the source, with a decay rate of $\sim$1.14 dB/$μ$m. We demonstrate the coherence between acoustic phonons generated from two distant sources through spatio-temporal interference. This concept could be scaled up to a larger number of sources, which enable a new generation of optically programmed, reconfigurable nanoacoustic devices and applications.

cond-mat.mes-hall↗

arXiv2022

Probing Gigahertz Coherent Acoustic Phonons in TiO$_{2}$ Mesoporous Thin Films

Ultrahigh-frequency acoustic-phonon resonators usually require atomically flat interfaces to avoid phonon scattering and dephasing, leading to expensive fabrication processes, such as molecular beam epitaxy. In contrast, mesoporous thin films are based on inexpensive wet chemical fabrication techniques. Here, we report mesoporous titanium dioxide-based acoustic resonators with resonances up to 90 GHz, and quality factors from 3 to 7. Numerical simulations show a good agreement with the picosecond ultrasonics experiments. We also numerically study the effect of changes in the speed of sound on the performance of the resonator. This change could be induced by liquid infiltration into the mesopores. Our findings constitute the first step towards the engineering of building blocks based on mesoporous thin films for reconfigurable optoacoustic sensors.

cond-mat.mes-hall↗

arXiv2022

Diffusion of photo-excited holes in viscous electron fluid

The diffusion of photo-generated holes is studied in a high-mobility mesoscopic GaAs\ channel where electrons exhibit hydrodynamic properties. It is shown that the injection of holes into such an electron system leads to the formation of a hydrodynamic three-component mixture consisted of electrons and photo-generated heavy and light holes. The obtained results are analyzed within the framework of ambipolar diffusion, which reveals characteristics of a viscous flow. Both hole types exhibit similar hydrodynamic characteristics. In such a way the diffusion lengths, ambipolar diffusion coefficient and the effective viscosity of the electron-hole system are determined.

cond-mat.mes-hall↗

arXiv2020

Determination of carrier density and dynamics via magneto-electroluminescence spectroscopy in resonant tunneling diodes

We study the magneto-transport and magneto-electroluminescence properties of purely n-doped GaAs/Al$_{0.6}$Ga$_{0.4}$As resonant tunneling diodes with an In$_{0.15}$Ga$_{0.85}$As quantum well and emitter prewell. Before the resonant current condition, magneto-transport measurements reveal charge carrier densities comparable for diodes with and without the emitter prewell. The Landau level splitting is observed in the electroluminescence emission from the emitter prewell, enabling the determination of the charge carrier build-up. Our findings show that magneto-electroluminescence spectroscopy techniques provide useful insights on the charge carrier dynamics in resonant tunneling diodes and is a versatile tool to complement magneto-transport techniques. This approach will drive the way for developing potentially more efficient opto-electronic resonant tunneling devices, by e.g., monitoring voltage dependent charge accumulation for improving built-in fields and hence to maximize photodetector efficiency and/or minimize optical losses.

cond-mat.mtrl-sci↗

arXiv2019

Topology driven g-factor tuning in type-II quantum dots

We investigate how the voltage control of the exciton lateral dipole moment induces a transition from singly to doubly connected topology in type II InAs/GaAsSb quantum dots. The latter causes visible Aharonov-Bohm oscillations and a change of the exciton g-factor which are modulated by the applied bias. The results are explained in the frame of realistic $\mathbf{k}\cdot\mathbf{p}$ and effective Hamiltonian models and could open a venue for new spin quantum memories beyond the InAs/GaAs realm.

cond-mat.mes-hall↗

arXiv2019

Magnetically controlled exciton transfer in hybrid quantum dot-quantum well nanostructures

A magnetophotoluminescence study of the carrier transfer with hybrid InAs/GaAs quantum dot(QD)-InGaAs quantum well (QW) structures is carried out where we observe an unsual dependence of the photoluminescence (PL) on the GaAs barrier thickness at strong magnetic field and excitation density. For the case of a thin barrier the QW PL intensity is observed to increase at the expense of a decrease in the QD PL intensity. This is attributed to changes in the interplane carrier dynamics in the QW and the wetting layer (WL) resulting from increasing the magnetic field along with changes in the coupling between QD excited states and exciton states in the QW and the WL.

cond-mat.mes-hall↗

arXiv2018

Electroluminescence on-off ratio control of n-i-n GaAs/AlGaAs-based resonant tunneling structures

We explore the nature of the electroluminescence (EL) emission of purely n-doped GaAs/AlGaAs resonant tunneling diodes (RTDs) and the EL evolution with voltage. A singular feature of such a device is unveiled when the electrical output current changes from high to low and the EL on-off ratio is enhanced by 2 orders of magnitude compared to the current on-off ratio. By combining the EL and current properties, we are able to identify two independent impact ionization channels associated with the coherent resonant tunneling current and the incoherent valley current. We also perform the same investigation with an associated series resistance, which induces a bistable electrical output in the system. By simulating a resistance variation for the current-voltage and the EL, we are able to tune the EL on-off ratio by up to 6 orders of magnitude. We further observe that the EL on and off states can be either direct or inverted compared to the tunneling current on and off states. This electroluminescence, combined with the unique RTD properties such as the negative differential resistance (NDR) and high frequency operation, enables the development of high speed functional opto-electronic devices and optical switches.

cond-mat.mtrl-sci↗