arXiv subjects

G. Medeiros-Ribeiro

Publications and source records attributed to G. Medeiros-Ribeiro.

14 recordsLinked to original sources

arXiv2008

Determination of spin polarization in InAs/GaAs self-assembled quantum dots

The spin polarization of electrons trapped in InAs self-assembled quantum dot ensembles is investigated. A statistical approach for the population of the spin levels allows one to infer the spin polarization from the measure values of the addition energies. From the magneto-capacitance spectroscopy data, the authors found a fully polarized ensemble of electronic spins above 10 T when $\mathbf{B}\parallel[001]$ and at 2.8 K. Finally, by including the g-tensor anisotropy the angular dependence of spin polarization with the magnetic field $\mathbf{B}$ orientation and strength could be determined.

cond-mat.mtrl-sci↗

arXiv2007

Absorptive and dispersive optical responses of excitons in a single quantum dot

We have determined both the real and imaginary parts of the dielectric polarizability of a single quantum dot. The experiment is based on the observation and the manipulation of Rayleigh scattering at photon frequencies near the resonance of an optical exciton transition in single self-assembled InAs and InGaAs quantum dots. The interference between the narrow-band laser field and the weak electromagnetic field coherently scattered by the quantum dot is detected with a cryogenic Fabry-Perot setup by combined differential transmission and reflectivity measurements.

cond-mat.mes-hall↗

arXiv2007

Polarization-selective excitation of N-V centers in diamond

The nitrogen-vacancy (N-V) center in diamond is promising as an electron spin qubit due to its long-lived coherence and optical addressability. The ground state is a spin triplet with two levels ($m_s = \pm 1$) degenerate at zero magnetic field. Polarization-selective microwave excitation is an attractive method to address the spin transitions independently, since this allows operation down to zero magnetic field. Using a resonator designed to produce circularly polarized microwaves, we have investigated the polarization selection rules of the N-V center. We first apply this technique to N-V ensembles in [100] and [111]-oriented samples. Next, we demonstrate an imaging technique, based on optical polarization dependence, that allows rapid identification of the orientations of many single N-V centers. Finally, we test the microwave polarization selection rules of individual N-V centers of known orientation.

cond-mat.other↗

arXiv2007

Lande g-tensor in semiconductor nanostructures

Understanding the electronic structure of semiconductor nanostructures is not complete without a detailed description of their corresponding spin-related properties. Here we explore the response of the shell structure of InAs self-assembled quantum dots to magnetic fields oriented in several directions, allowing the mapping of the g-tensor modulus for the s and p shells. We found that the g-tensors for the s and p shells show a very different behavior. The s-state in being more localized allows the probing of the confining potential details by sweeping the magnetic field orientation from the growth direction towards the in-plane direction. As for the p-state, we found that the g-tensor modulus is closer to that of the surrounding GaAs, consistent with a larger delocalization. These results reveal further details of the confining potentials of self-assembled quantum dots that have not yet been probed, in addition to the assessment of the g-tensor, which is of fundamental importance for the implementation of spin related applications.

cond-mat.mtrl-sci↗

arXiv2007

Alloying mechanisms for epitaxial nanocrystals

The different mechanisms involved in the alloying of epitaxial nanocrystals are reported in this letter. Intermixing during growth, surface diffusion and intra-island diffusion were investigated by varying the growth conditions and annealing environments during chemical vapor deposition. The relative importance of each mechanism was evaluated in determining a particular composition profile for dome-shaped Ge:Si (001) islands. For samples grown at a faster rate, intermixing during growth was reduced. Si surface diffusion dominates during H$_2$ annealing whereas Ge surface diffusion and intra-island diffusion prevail during annealing in a PH$_3$ environment.

cond-mat.mtrl-sci↗

arXiv2004

Atomic ordering in self-assembled Ge:Si(001) islands observed by X-ray scattering

X-ray diffuse scattering in the vicinity of a basis-forbidden (200) Bragg reflection was measured for a sample with uncapped self-assembled Ge islands epitaxially grown on Si(001). Our results provide evidence of atomically ordered SiGe domains in both islands and wetting layer. The modeling of x-ray profiles reveals the presence of antiphase boundaries separating the ordered domains in a limited region of the islands where the stoichiometry is close to Si0.5Ge0.5.

cond-mat.mtrl-sci↗

arXiv2003

Aharonov-Bohm signature for neutral excitons in type-II quantum dot ensembles

It is commonly believed that the Aharonov-Bohm (AB) effect is a typical feature of the motion of a charged particle interacting with the electromagnetic vector potential. Here we present a magnetophotoluminescence study of type-II InP/GaAs self-assembled quantum dots, unambiguously revealing the Aharonov-Bohm-type oscillations for neutral excitons when the hole ground state changes its angular momentum from lh = 0 to lh = 1, 2, and 3. The hole ring parameters derived from a simple model are in excellent agreement with the structural parameters for this system.

cond-mat.mes-hall↗

arXiv2003

g-factor engineering and control in self-assembled quantum dots

The knowledge of electron and hole g-factors, their control and engineering are key for the usage of the spin degree of freedom for information processing in solid state systems. The electronic g-factor will be materials dependent, the effect being larger for materials with large spin-orbit coupling. Since electrons can be individually trapped into quantum dots in a controllable manner, they may represent a good platform for the implementation of quantum information processing devices. Here we use self-assembled quantum dots of InAs embedded in GaAs for the g-factor control and engineering.

cond-mat.mes-hall↗

arXiv2001

Transport signatures of correlated disorder in a two-dimensional electron gas

We report electronic transport measurements on two-dimensional electron gases in a Ga[Al]As heterostructure with an embedded layer of InAs self-assembled quantum dots. At high InAs dot densities, pronounced Altshuler-Aronov-Spivak magnetoresistance oscillations are observed, which indicate short-range ordering of the potential landscape formed by the charged dots and the strain fields. The presence of these oscillations coincides with the observation of a metal-insulator transition, and a maximum in the electron mobility as a function of the electron density. Within a model based on correlated disorder, we establish a relation between these effects.

cond-mat.mes-hall↗

arXiv1998

Metal-Insulator Transition in a Disordered Two-Dimensional Electron Gas in GaAs-AlGaAs at zero Magnetic Field

A metal-insulator transition in two-dimensional electron gases at B=0 is found in Ga(Al)As heterostructures, where a high density of self-assembled InAs quantum dots is incorporated just 3 nm below the heterointerface. The transition occurs at resistances around h/e^2 and critical carrier densities of 1.2 10^11cm^-2. Effects of electron-electron interactions are expected to be rather weak in our samples, while disorder plays a crucial role.

cond-mat.mes-hall↗

arXiv1996

Far-infrared and capacitance spectroscopy of self-assembled InAs quantum dots

We review a number of recent experiments which are probing ground state and excitations of few-electron systems in self-assembled InAs quantum dots. Far-infrared spectroscopy, together with local as well as large-scale capacitive probing allows for a detailed investigation of the different contributions to the many-particle spectrum in the dots. The influence of electron--electron interactions on the ground state and the excitations is discussed.

cond-mat↗

arXiv1996

Single-electron charging of self-assembled InAs quantum dots

The many-particle ground state and excitations of self-assembled InAs quantum dots are investigated using far-infrared (FIR) and capacitance spectroscopy. The contributions of quantization and charging energies to the $n$--electron energy spectrum are determined. For $n = 1$, 2, we find good agreement with a parabolic model; for higher filling, the Coulomb interaction reveals itself not only in the capacitance, but also in the FIR excitations

cond-mat↗

arXiv1996

Shell structure and electron-electron interaction in self-assembled InAs quantum dots

Using far-infrared spectroscopy, we investigate the excitations of self-organized InAs quantum dots as a function of the electron number per dot, 1<n<6, which is monitored in situ by capacitance spectroscopy. Whereas the well-known two-mode spectrum is observed when the lowest s - states are filled, we find a rich excitation spectrum for n=3, which reflects the importance of electron-electron interaction in the present, strongly non-parabolic confining potential. From capacitance spectroscopy we find that the electronic shell structure in our dots gives rise to a distinct pattern in the charging energies which strongly deviates from the monotonic behavior of the Coulomb blockade found in mesoscopic or metallic structures.

cond-mat↗

arXiv1996

Single-Electron Charging and Coulomb Interaction in InAs Self-Assembled Quantum Dot Arrays

Sequential single-electron charging is observed in InAs Self-Assembled Quantum Dots using capacitance spectroscopy. In this system, the Coulomb energy is smaller than the inter-level energy spacings due to the quantum confinement and both effects can be separately identified. A theoretical model is proposed for this system and the capacitance experiments were devised in order to experimentally observe the effects of Coulomb interaction between electrons on the dots. The effects of inter- and intra-dot Coulomb interaction have been observed in the capacitanc e spectra. A good agreement between the proposed model and experiment is achieved.

cond-mat↗