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A gestão de visitação em áreas protegidas age em duas frentes, em geral desconexas: a social e a biofísica. Na prática, a dicotomia entre gestão de segurança e de impactos da visitação transparece no uso de ferramentas díspares que inibe uma ou outra de acordo com a visão e capacitação das equipes envolvidas. Este trabalho propõe sistematizar uma visão integradora onde a qualidade da experiência da visitação, do ponto de vista da segurança da atividade, e as alterações ambientais diretas ou indiretas subsequentes possam ser ponderadas, avaliadas e geridas simultaneamente dentro de um Sistema de Gestão de Segurança e Impactos.

The inertia of trapping and detrapping of nonequilibrium charge carriers affects the electrochemical and transport properties of both bulk and nanoscopic structures in a very peculiar way. An emerging memory response with a hysteresis in the current-voltage response and its eventual multiple crossing, produced by this universally available ingredient, are signatures of this process. Here, we deliver a microscopic and analytical solution for these behaviors, understood as the modulation of the topology of the current-voltage loops. The memory emergence becomes thus a characterization tool for intrinsic features that affect the electronic transport of solids such as the nature and number of trapping sites, intrinsic symmetry constraints, and natural relaxation time scales. This method is also able to reduce the seeming complexity of frequency-dependent electrochemical impedance and cyclic voltammetry observable for a variety of systems to a combination of simple microscopic ingredients., Comment: 9 pages, 7 figures. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Journal of Applied Physics 133, 134901 (2023) and may be found at https://aip.scitation.org/doi/full/10.1063/5.0142721

We report a comprehensive theory to describe exciton and biexciton valley dynamics in monolayer Mo1−xWxSe2 alloys. To probe the impact of different excitonic channels, including bright and dark excitons, intravalley biexcitons, intervalley scattering between bright excitons, as well as bright biexcitons, we have performed a systematic study from the simplest system to the most complex one. In contrast to the binary WSe2 monolayer with weak photoluminescence (PL) and high valley polarization at low temperatures and the MoSe2, that presents high PL intensity, but low valley polarization, our results demonstrate that it is possible to set up a ternary alloy with intermediate W-concentration that holds simultaneously a considerably robust light emission and an efficient optical orientation of the valley pseudospin. We find the critical value of W-concentration, xc, that turns alloys from bright to darkish. The dependence of the PL intensity on temperature shows three regimes: while bright monolayer alloys display a usual temperature dependence in which the intensity decreases with rising temperature, the darkish alloys exhibit the opposite behavior, and the alloys with x around xc show a non-monotonic temperature response. Remarkably, we observe that the biexciton enhances significantly the stability of the exciton emission against fluctuations of W-concentration for bright alloys. Our findings pave the way for developing high-performance valleytronic and photo-emitting devices.

The characterization of helical states can be performed by checking the existence of the re-entrant behaviour, which appears as a dip in the conductance probed in nanowires (NWs) with strong spin-orbit coupling (SOC) and under perpendicular magnetic field. On the other hand, the experiment described in Ref. 1 observed the re-entrant behaviour in the absence of a magnetic field, which was explained through spin-flipping two-particle backscattering. We theoretically show that the observation of the re-entrant behaviour is due to a multi-channel scattering mechanism, which causes a reduction of the transmission when an effective attractive potential and coupling between different channels are present. Both ingredients are provided by the SOC in the transport properties of NWs., 5 pages, 4 figures

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., 9 pages, 7 figures

Owing to nonzero charge and spin degrees of freedom, trions offer unprecedented tunability and open new paths for applications in devices based on 2D semiconductors. However, in monolayer WSe

A comprehensive study of excitonic complexes in high-quality GaAs quantum wells has been performed. The polarization-resolved photoluminescence results show exciton, biexciton, and trion emissions tuned by temperature, excitation power, and by an external magnetic field. Excitons and biexcitons show important differences in their dependence on the external field. While the Zeeman splitting of biexcitons depends monotonically on the magnetic field, with a nearly constant g-factor, the behaviour of the exciton energy splitting is nonmonotonic and includes an inversion of sign as a function of the magnetic field. More importantly, we observe that a trion resonance emerges at a finite magnetic field, and only appears at low laser excitation power and for σ+ polarization emission. The non-trivial dependence of the energy levels on the external magnetic field, together with the polarization selective trion emission, leads to an intricate exciton and trion dynamics, which can be reproduced by a set of coupled rate equations. Based on this theoretical approach, we show that a fast spin-flip process can lead to the spin-asymmetric emission, which reveals a contrasting spin-dynamics of excitonic complexes ruled by their charge.

The interest in light-sensitive organic molecules, such as azobenzene, has increased because of their ability to functionalize two-dimensional layered systems and engineer their electronic structure. In this work, we explore the azobenzene trans and cis isomer adsorption on a molybdenum disulfide MoS2(0001) layer employing the density functional theory (DFT) within van der Waals (vdW) corrections to the semilocal exchange–correlation functional. We found that the aromatic rings of azobenzene lay parallel to the surface (two in the trans isomer and one in the cis isomer), which contributes to increasing the configuration stability by vdW interactions. Furthermore, we found a relatively large work function change upon adsorption because of the electron density rearrangement, and hence, it might affect the electronic transport properties within the single MoS2(0001) layer. We observed an increase in the relative DFT + vdW total energy among the azobenzene isomers (trans and cis) from 0.51 eV in the gas-phase...

Structural and electronic changes induced by laser irradiation are currently of interest owing to the possibility to tune the mechanical, optical, and transport properties of the irradiated materials. In this work, we investigate the effects of laser irradiation on indium phosphide, InP, by modifying the electronic temperature, T e, of the system within the density functional theory framework and performing molecular dynamics simulations to prove that the laser irradiation also provokes a local thermalization effect. We found that the process can be described by a two-stage mechanism. First, at low T e values (0–1.0 eV), the laser energy induces electronic transitions, while the InP lattice remains undisturbed and cool. In the second stage (with T e in the range of 1.0–4.0 eV), both electron-electron scattering and electron-phonon coupling processes are triggered, increasing the energy of the lattice so as to provoke a Coulomb explosion, which changes some physical chemical properties of InP. The close agreement between the simulations helps explain the formation of metallic In as it is observed in the transmission electron microscopy images.

The identification of physical parameters that lead to magnetism in apparent nonmagnetic semiconductor systems has continuously challenged our community. In particular, for quantum-dot systems, they are key factors that contribute to their magneto-optical properties. We report, experimentally, optical evidences of induced nanomagnetism in nonmagnetic CdSe quantum dots and assess theoretically the role played by charged and uncharged vacancies. The analysis of these effects rests upon both the chemical and strain environments where the quantum dots are embedded. The interplay of spin-orbit interaction with built-in axial strains has been demonstrated to be a key factor for the magnetic moment alignment. This has been achieved in this paper by emulating the electronic structure at atomistic levels, considering various defect configurations and taking into account both the quantum dot composition and the influence of the host lattice. Postprint

Surface functionalization emerges as an alternative pathway for electronic structure engineering in two-dimensional (2D) systems. We explore a hybrid heterostructure built from a 2D transition-metal dichalcogenide atop a layer of photochromic self-assembled azobenzene molecules. This setup can modify carrier transport through the 2D nanosheet by an effective photoactived gating control, achieved through trans to cis isomerization of the azobenzene in close contact with the 2D nanosheet. We show theoretically that this behavior can be ascribed to a tunable gating mechanism. We use a combination of atomistic calculations of the local effective potential profile with simulations of the electron scattering by such potential in a massive Dirac Hamiltonian formalism. We find that different isomers induce a local perturbation with drastically different features that explain well the experimental behavior.

The original Pascaline was a mechanical calculator able to sum and subtract integers. It encodes information in the angles of the mechanical components (such as wheels and cylinders), is aided by gravity, and performs the calculations. Here, we show that such a concept can be realized in electronics using memory elements such as memristive systems. By using memristive emulators, we have demonstrated experimentally the memcomputing version of the mechanical Pascaline, capable of processing and storing the numerical results in the multiple levels of each memristive element. Our result is the first experimental demonstration of multidigit arithmetic with multilevel memory devices that further emphasize the versatility and potential of memristive systems for future on-chip information processing and storage architectures.

We have studied the nature and character switching of relativistic bound states in quantum dot–ring structures produced by a set of circular concentric metallic gates on a graphene sheet placed over a substrate. The structure consists of an attractive core, a repulsive barrier and an attractive rim region where the resulting potential profiles and the interaction between the graphene layer and substrate are treated within a modified Dirac Hamiltonian describing the system. Our simulations allow a microscopic mapping of the character of electron and hole quasi-particle states and, in this environment, we study the effects of mixing between states in the dot–ring structure. Unusual electronic properties are reported by the emergence of localized states in the barrier region where electrons behave like holes in the inverted well potential and, as a direct consequence, the appearance of intertwined energy levels is envisaged which are tuned by bias voltages and the effective strength of the graphene–substrate interaction. The optical selection rules and the light absorption in effective gap regions between localized carrier states have been characterized and linked to the wavefunction engineering.

Owing to nonzero charge and spin degrees of freedom, trions offer unprecedented tunability and open new paths for applications in devices based on 2D semiconductors. However, in monolayer WSe2, the trion photoluminescence is commonly detected only at low temperatures and vanishes at room temperature, which undermines practical applications. To unveil how to overcome this obstacle, we have developed a comprehensive theory to probe the impact of different excitonic channels on the trion emission in WSe2 monolayers, which combines ab initio tight-binding formalism, Bethe-Salpeter equation and a set of coupled rate equations to describe valley dynamics of excitonic particles. Through a systematic study in which new scattering channels are progressively included, we found that, besides the low electron density, strong many-body correlations between bright and dark excitonic states quenches the trion emission in WSe2. Therefore, the reduction of scatterings from bright to dark states is required to achieve trion emission at room temperature for experimentally accessible carrier concentrations.

We have studied the optical and electronic transport properties of n-type AlSb/GaInAsSb double barrier quantum well resonant tunneling diodes (RTDs). The RTDs were grown by molecular beam epitaxy on GaSb substrates. Collector, quantum well, and emitter regions are comprised of the lattice-matched quaternary semiconductor Ga0.64In0.36As0.33Sb0.67. Photoluminescence emission spectra reveal a direct bandgap semiconductor with a bandgap energy of Eg≈0.37 eV, which corresponds to a cut-off wavelength of λ≈3.3 μm. The composition-dependent bandgap energy is found to follow Shim’s model. At room temperature, we observe resonance current densities of jres=0.143 kA cm−2 with peak-to-valley current ratios of up to PVCR=6.2. At cryogenic temperatures T

Electronic transport through a material depends on the response to local perturbations induced by defects or impurities in the material. The scattering processes can be described in terms of phase shifts and corresponding cross sections. The multiorbital nature of the spinor states in transition metal dichalcogenides would naturally suggest the consideration of a massive Dirac equation to describe the problem, while the parabolic dispersion of its conduction and valence bands would invite a simpler Schrodinger equation description. Here, we contrast the scattering of massive Dirac particles and Schrodinger electrons, in order to assess different asymptotic regimes (low and high Fermi energy) for each one of the electronic models and describe their regime of validity or transition. At low energies, where the dispersion is approximately parabolic, the scattering processes are dominated by low angular momentum channels, which results in nearly isotropic scattering amplitudes. On the other hand, the differential cross section at high Fermi energies exhibits clear signatures of the linear band dispersion, as the partial phase shifts approach a non-zero value. We analyze the electronic dynamics by presenting differential cross sections for both attractive and repulsive scattering centers. The dissimilar behavior between Dirac and Schrodinger carriers points to the limits and conditions over which different descriptions are required for the reliable treatment of scattering processes in these materials.

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 higher to lower values and the EL on-off ratio is enhanced by two orders of magnitude compared to the current on-off ratio. By combining the EL and the 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 six orders of magnitude. We further observe that the EL on and off states can be either direct or inverted compared to the tunneling current of the on and off states. This electroluminescence, combined with the unique RTD properties, such as the negative differential resistance and high-frequency operation, enables the development of high-speed functional optoelectronic devices and optical switches.

The optimal quantum control theory is employed to determine electric pulses capable of producing quantum gates with high fidelity (higher than 0.9997). Particularly, these quantum gates were chosen to perform the permutation algorithm (Z. Gedik et al., Scientific reports 5, 14671, (2015).) in hybrid qubits in a double quantum dot (DQD) platform. The permutation algorithm is an oracle based quantum algorithm that solves the problem of the permutation parity faster than a classical algorithm without the necessity of entanglement between particles. The only requirement for achieving the speedup is the use of a one-particle quantum system with at least three levels. The high fidelity found in our results is closely related to quantum speed limit, which is a measure of how fast a quantum state can be manipulated. Furthermore, our scheme can be used for the practical realization of different quantum algorithms in DQDs., 5 pages, 5 figures, comments welcome

We present an experimental and theoretical study about the carrier confinement geometry and topology in InAs/GaAsSb quantum dots. The investigated sample consists of a field-effect device embedding a single layer of dot-in-a-well InAs/GaAsSb nanostructures. These nanostructures exhibit large electron-hole dipole moments and radiative lifetimes under externally applied electric fields. Both phenomena are related to the type-II band alignment existing between the two materials which, in principle, could also result in a change of the hole orbital confinement topology from simply to doubly connected. The latter aspect will be confirmed by ensemble magnetophotoluminescence experiments at 4.2 K. The oscillations observed in the photoluminescence intensity and degree of circular polarization will be described by an axially symmetric \(\mathbf {k}\cdot \mathbf {p}\) model combining vertical electric and magnetic fields. Due to the large spin-orbit coupling of III-Sb nanostructures, the modulation of the orbital confinement geometry and topology reported here shall open a venue to control the spin dynamics by external voltages. This exciting idea will be theoretically discussed through band-effective models including spin-orbit coupling and anisotropic confinement effects.

The authors are grateful for financial support by the BMBF via national project EIPHRIK (FKZ: 13N10710), the European Union (FPVII (2007-2013) under grant agreement No. 256959 NANOPOWER and No. 318287 LANDAUER), and the Brazilian Agencies FAPESP (2013/24253-5, 2012/13052-6, and 2012/51415-3), CNPq and CAPES. Sensor miniaturization together with broadening temperature sensing range are fundamental challenges in nanothermometry. By exploiting a large temperature-dependent screening effect observed in a resonant tunneling diode in sequence with a GaInNAs/GaAs quantum well, we present a low dimensional, wide range, and high sensitive nanothermometer. This sensor shows a large threshold voltage shift of the bistable switching of more than 4.5 V for a temperature raise from 4.5 to 295 K, with a linear voltage-temperature response of 19.2 mV K-1, and a temperature uncertainty in the millikelvin (mK) range. Also, when we monitor the electroluminescence emission spectrum, an optical read-out control of the thermometer is provided. The combination of electrical and optical read-outs together with the sensor architecture excel the device as a thermometer with the capability of noninvasive temperature sensing, high local resolution, and sensitivity. Postprint

We report the energy spectrum and the eigenstates of conduction and uncoupled valence bands of a quantum well under the influence of a tilted magnetic field. In the framework of the envelope approximation, we implement two analytical approaches to obtain the nontrivial solutions of the tilted magnetic field: (a) the Bubnov-Galerkin spectral method and b) the perturbation theory. We discuss the validity of each method for a broad range of magnetic field intensity and orientation as well as quantum well thickness. By estimating the accuracy of the perturbation method, we provide explicit analytical solutions for quantum wells in a tilted magnetic field configuration that can be employed to study several quantitative phenomena.

Combining atomistic methods and effective mass approaches, the magnetic field response of Mn-doped deformed quantum dots has been characterized. The defect-induced asymmetry triggers unavoidable spin-orbit coupling effects that become more relevant the smaller the quantum confinement. Thus, the expected spin splitting modulation by the exchange interaction between the confined carriers and the Mn impurity is tuned by the intertwining of spatial geometry and magnetic field. Furthermore, ab initio calculations are presented for assessing the exchange interaction term and its response to confinement effects at the atomistic level.

The authors are grateful for financial support by the European Union (FPVII (2007-2013) under grant agreement no. 318287 LANDAUER), and the Brazilian Agencies FAPESP (grants 2012/13052 - 6, and 2012/51415 - 3), CNPq and CAPES. V. L.-R. acknowledges the support of FAPESP (grant: 2014/02112-3). Y.V.P. was supported by National Science Foundation grant ECCS-1202383. Electronic circuits composed of one or more elements with inherent memory - memristors, memcapacitors and meminductors - offer lower circuit complexity and enhanced functionality for certain computational tasks. Networks of these elements are proposed for novel computational paradigms that rely on information processing and storage on the same physical platform. We show a nanoscaled memdevice able to act as an electronic analogue of tipping buckets that allows reducing the dimensionality and complexity of a sensing problem by transforming it into a counting problem. The device offers a well adjustable, tunable and reliable periodic reset that is controlled by theamounts of transferred quantum dot charges per gate voltage sweep. When subjected to periodic voltage sweeps the quantum dot (bucket) may require up to several sweeps before a rapid full discharge occurs thus displaying period doubling, period tripling and so on between self-governing reset operations. Postprint Postprint

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/GaAsxSb1−x 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 →k⋅→p and effective Hamiltonian models and could open a venue for new spin quantum memories beyond the InAs/GaAs realm., The authors gratefully acknowledge financial support from EURAMET through EMPIR program 17FUN06-SIQUST, from Spanish MINEICO through Grants No. TEC2015-64189-C3-2-R, No. MAT2016-77491-C2-1-R, No. EUIN2017-88844, and No. RYC-2017-21995, from Comunidad de Madrid through Grant No. P2018/EMT-4308, and from CSIC through Grants No. I-COOP-2017-COOPB20320 and No. PTI-001. Support from Brazilian agencies is also acknowledged through FAPESP Grant No. 2014/02112-3 and CNPq Grant No. 306414/2015-5.

The authors gratefully acknowledge financial support from the European Union (FPVII (2007-2013) under Grant Agreement No. 318287 Landauer) as well as the State of Bavaria. The Brazilian authors acknowledge the support from CNPq. V.L.-R. acknowledges the support from FAPESP (Grant Nos. 2014/02112-3 and 2015/10765-0). We report the optical control of localized charge on positioned quantum dots in an electro-photo-sensitive memristor. Interband absorption processes in the quantum dot barrier matrix lead to photo-generated electron-hole-pairs that, depending on the applied bias voltage, charge or discharge the quantum dots and hence decrease or increase the conductance. Wavelength-dependent conductance control is observed by illumination with red and infrared light, which leads to charging via interband and discharging via intraband absorption. The presented memristor enables optical conductance control and may thus be considered for sensory applications in artificial neural networks as light-sensitive synapses or optically tunable memories. Postprint

This work reports evidence of the induced migration of Mn 2+ ions in Cd (1− x ) Mn x S nanocrystals (NCs) by selecting a specific thermal treatment for each sample. The growth and characterization of these magnetic dots were investigated by atomic force microscopy (AFM), optical absorption (OA), and electronic paramagnetic resonance (EPR) techniques. The comparison of experimental and simulated EPR spectra confirms the incorporation of Mn 2+ ions both in the core and at the dot surface regions. The thermal treatment of a magnetic sample, via selected annealing temperature and/or time, affects the fine and hyperfine interaction constants which modify the shape and the intensity of the EPR transition spectrum. The identification of these changes has allowed tracing the magnetic ion migration from core to surface regions of a dot as well as inferring the local density of the magnetic impurity ions.

The structural properties of twin-plane superlattices in InP nanowires are systematically analyzed. First, we employ molecular dynamics simulations to determine the strain fields in nanowires grown in the [111] direction. These fields are produced by the formation of twin-planes and by surface effects. By using the stress tensor obtained from molecular dynamics simulations, we are able to describe changes on the electronic structure of these nanowires. On the basis of the resulting electronic structure, we confirm that a one-dimensional superlattice is indeed formed. Furthermore, we describe the transport properties of both electrons and holes in the twin-plane superlattices. In contrast to the predicted transparency of Γ-electrons in heterolayered III-V semiconductor superlattices, we verify that surface effects in 1D systems open up possibilities of electronic structure engineering and the modulation of their transport and optical responses.

We have achieved conditions to obtain optical memory effects in semiconductor nanostructures. The system is based on strained InP quantum wires where the tuning of the heavy-light valence band splitting has allowed the existence of two independent optical channels with correlated and uncorrelated excitation and light-emission processes. The presence of an optical channel that preserves the excitation memory is unambiguously corroborated by photoluminescence measurements of free-standing quantum wires under different configurations of the incoming and outgoing light polarizations in various samples. High-resolution transmission electron microscopy and electron diffraction indicate the presence of strain effects in the optical response. By using this effect and under certain growth conditions, we have shown that the optical recombination is mediated by relaxation processes with different natures: one a Markov and another with a non-Markovian signature. Resonance intersubband light-heavy hole transitions assisted by optical phonons provide the desired mechanism for the correlated non-Markovian carrier relaxation process. A multiband calculation for strained InP quantum wires was developed to account for the description of the character of the valence band states and gives quantitative support for light hole-heavy hole transitions assisted by optical phonons.

We describe the effects of spin–orbit contribution in the presence of a uniform axial electric field on the electronic structure of single electron quantum rings in addition to the conventional Stark effect. The spin-split levels are obtained by considering the spatial asymmetries induced by the Rashba and the Dresselhaus spin–orbit interactions on the spinor states. The quantum-ring flat geometry allows us to study the spin-hybridization effects induced by spin–orbit coupling under a wide range of values of the axial electric field. The influence of the peculiar axial and perpendicular confinements in the structure on the spin orientation, the azimuthal component of the angular momentum and their coupling to the external fields is discussed in details for two materials.

We study the role of different orientations of an applied magnetic field as well as the interplay of structural asymmetries on the characteristics of eigenstates in a quantum ring system. We use a nearly analytical model description of the quantum ring, which allows for a thorough study of elliptical deformations and their influence on the spin content and Berry phase of different quantum states. The diamagnetic shift and Zeeman interaction compete with the Rashba spin-orbit interaction, induced by confinement asymmetries and external electric fields, to change spin textures of the different states. Smooth variations in the Berry phase are observed for symmetric quantum rings as function of applied magnetic fields. Interestingly, we find that asymmetries induce nontrivial Berry phases, suggesting that defects in realistic structures would facilitate the observation of geometric phases.

The interplay between structural properties and charge transfer in self-assembled quantum ring (QR) chains grown by molecular beam epitaxy on top of an InGaAs/GaAs quantum dot (QD) superlattice template is analyzed and characterized. The QDs and QRs are vertically stacked and laterally coupled as well as aligned within each layer due to the strain field distributions that governs the ordering. The strong interdot coupling influences the carrier transfer both along as well as between chains in the ring layer and dot template structures. A qualitative contrast between different dynamic models has been developed. By combining temperature and excitation intensity effects, the tuning of the photoluminescence gain for either the QR or the QD mode is attained. The information obtained here about relaxation parameters, energy scheme, interlayer and interdot coupling resulting in creation of 1D structures is very important for the usage of such specific QR–QD systems for applied purposes such as lasing, detection, and energy-harvesting technology of future solar panels.

We have analyzed how the symmetries and the anisotropies of energy dispersions and of the spinor states, within full spin-orbit interaction, form the two independent circular spin polarizations. We also compare how the effects produced by Rashba and Dresselhauss interaction terms act on the structure of the Hilbert space. These aspects are used to envisage a voltage controlled multichannel spin-filtering regime in nonmagnetic diode structures.

We discuss how symmetries and anisotropies of electron states, within full spin–orbit coupling, form independent circular polarization spinors. The aspects of a voltage controlled multichannel spin-filtering regime is discussed.

We present a systematic theoretical study of the effective Zeeman spin- and non-linear-splitting of a single spherical quantum dot based on the Hamiltonian model. The effect of spin-hybridization on conduction band states is pointed out as the main source of the strong dependence of Lande factors and effective masses on external fields. The topology of the electronic orbitals is highly sensitive to the magnetic field tuning and to the spin polarization. The electron, hole and excitonic g-factors, as well as the diamagnetic coefficient are calculated for CdTe semiconductor quantum dots. Different systematic experimental methods are proposed in order to determine the behaviour of the electronic properties under analysis as a function of magnetic field and confinement geometry. Complementary optical transitions, in Faraday and Voigt configurations, can be used in the determination of electron, hole and exciton Lande factors, effective magnetic masses and diamagnetic coefficients.

The Zeeman splitting in a single CdTe quantum dot (QD) is theoretically analyzed in the frame of Kane-Weiler 8 × 8 k · p model. The conduction g-factor was calculated as a function of the QD size. We discuss the effects of the dot geometry on the magnitude and on sign of the g-factor, that opens new channels towards control and manipulation of magneto-optical properties and spin in different confinement regimes. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We present a systematic theoretical study, based on the Kane-Weiler 8 x 8 k p model, of the linear Zeeman splitting introduced by the interaction between the angular momentum and the magnetic field which can give a measure of the non-linear Zeeman effect associated with interband coupling and diamagnetic contributions. The conduction and valence bands g-factors are calculated for InSb spherical and semi-spherical quantum dots. The calculations of the g-factors showed an almost linear dependence, for the ground state, on the magnetic field. We have also found that the strong magnetic field dependence as well as the dependence on the dot size of the effective spin splitting can be unambiguously attributed to the strength of the inter-level mixing.

The 8 x 8 k.p Kane-Weiler model has been extended to study narrow-gap semiconductor quantum wells in the presence of a magnetic field. It is shown that the study of the inherent symmetry in this Hamiltonian model permits a suitable separation of the solution into two orthogonal Hilbert sub-spaces. The electronic properties are evaluated as function of Kane-Luttinger parameters, magnetic field strength, and Landau level number. The selection rules and anomalies in the conduction Zeeman splitting observed in the interband magneto-optical absorption spectrum are analyzed for the Faraday and Voigt geometry configurations. Due to strong intra- and interband admixtures in narrow-gap materials, spin-flip-like transitions are predicted to occur in the magneto-optical spectrum of HgCdTe/CdTe quantum well solid solutions.

The authors are grateful for financial support by the BMBF via national project EIPHRIK (FKZ: 13N10710), the European Union (FPVII (2007-2013) under grant agreement no. 318287 LANDAUER), and the Brazilian Agencies CNPq and CAPES. S. H. gratefully acknowledges support by the Royal Society and the Wolfson Foundation. We study the electroluminescence (EL) emission of purely n-doped resonant tunneling diodes in a wide temperature range. The paper demonstrates that the EL originates from impact ionization and radiative recombination in the extended collector region of the tunneling device. Bistable current-voltage response and EL are detected and their respective high and low states are tuned under varying temperature. The inversion bistability of the EL intensity can be switched from direct to inverted with respect to the tunneling current and the optical on/off ratio can be enhanced with increasing temperature. One order of magnitude amplification of the optical on/off ratio can be attained compared to the electrical one. Our observation can be explained by an interplay of moderate peak-to-valley current ratios, large resonance voltages, and electron energy loss mechanisms and thus could be applied as an alternative route towards optoelectronic applications of tunneling devices. Postprint

We present a theoretical description of Bogolyubov-type excitations of exciton-polariton Bose-Einstein condensates (BECs) in semiconductor microcavities. For a typical two-dimensional (2D) BEC we focus on two limiting cases, the weak-and strong-coupling regimes, where a perturbation theory and the Thomas-Fermi approximation, respectively, are valid. We calculate integrated scattering intensity spectra for probing the collective excitations of the condensate in both considered limits. Moreover, in relation to recent experiments on optical modulation allowing localization of condensates in a trap with well-controlled shape and dimensions, we study the quasi-one-dimensional (1D) motion of the BEC inmicrowires and report the corresponding Bogolyubov excitation spectrum. We show that in the 1D case the characteristic polariton-polariton interaction constant is expressed as g(1) = 3 lambda N/(2L(y)) (lambda is the 2D polariton-polariton interaction parameter in the cavity, N the number of the particles, and L-y the wire cavity width). We reveal some interesting features for 2D and 1D Bogolyubov spectra for both repulsive (lambda > 0) and attractive (lambda < 0) interactions., Fundação para a Ciência e a Tecnologia (FCT) - Portuguese Foundation for Science and Technology Grants: PTDC-FIS-113199-2009, PEst-C/FIS/UI0607/2013, CNPq, FAPESP, Brazil, Russian Ministry of Education and Science 11.G34.31.0067

A multiband theory of the dielectric response in a quasi-two dimensional (Q2D) electron plasma of narrow-gap semiconductor structures in an external magnetic field has been developed. The strong interband mixing plays an essential role in the determination of the shape and behavior of the dielectric response in narrow-band Q2D systems. We have used a full 8×8 k⋅p Hamiltonian model to describe the Landau levels. A rigorous theoretical analysis shows, among other interesting features, that spin–flip-like intrasubband transitions are allowed and its effects on the related optical properties of Q2D systems are investigated. The influence of the Landau level filling factor on the dielectric response and the limit of integer and fractional filling factors cases are discussed. We found that the occupation of Landau levels modulates the polarizability strength of the plasma.

In the frame of a full 8×8 k.p Hamiltonian, an exhaustive study of magneto-optical properties of narrow-gap semiconductor heterostructures has been developed. The effects of spatial confinement on the conduction Landau ladders of Hg1−xCdxTe/CdTe quantum wells are described. We report anomalous spin crossings of the Landau fan plots which lead to a sign inversion of the effective Lande factor as the magnetic field strength increases. Our quantitative explanation shows that the analyzed effects appear to be very sensitive to the temperature and the Cd-concentration of the sample. We discuss how the complemental aspect of the absorption coefficient obtained within Faraday and Voigt configurations may allow a direct evaluation of the anomaly in the g-factor as a function of the field.

An analytical model developed to describe the crystallization kinetics of spherical glass particles has been derived in this work. A continuous phase transition from three-dimensional (3D)-like to 1D-like crystal growth has been considered and a procedure for the quantitative evaluation of the critical time for this 3D-1D transition is proposed. This model also allows straightforward determination of the density of surface nucleation sites on glass powders using differential scanning calorimetry data obtained under different thermal conditions.

The Raman profiles are calculated as a function of magnetic field ${B}_{0}$ and the laser frequency ${\ensuremath{\omega}}_{L}$ for the Fr\"ohlich type of electron-phonon interaction in parallel scattering configurations with circularly polarized light $[\overline{z}({\ensuremath{\sigma}}^{\ifmmode\pm\else\textpm\fi{}},{\ensuremath{\sigma}}^{\ifmmode\pm\else\textpm\fi{}})z]$ spread in z along the [001] crystal direction. A $4\ifmmode\times\else\texttimes\fi{}4$ Luttinger Hamiltonian has been used in order to take the valence-band admixture into account. Explicit expressions for the Raman scattering efficiency as a function of ${\ensuremath{\omega}}_{L},$ ${B}_{0},$ and the Luttinger parameters are given. Different effects due to the band nonparabolicity and the mixing of valence-band states are discussed. For a realistic picture of the resonance profiles an explicit calculation of the lifetime broadening of the intermediate electronic states assisted by a LO phonon has been carried out including the dependence on the laser incident energy, magnetic field, and Landau quantum number. Results are applied to explain recent experimental data for GaAs.

Departament of Theoretical Physics, Havana University,Vedado 10400, CubaReceived30July 2006, accepted 18 August 2006Published online 7 February 2007PACS 75.50.Pp, 78.67.Hc, 85.70.SqWe have exploredanexchange-inducedpropertyoftheelectronicstructureofdilutedmagneticsemiconduc-tor quantum dots in order to propose an externally controlled optical switching device. Various confinementshapes, dot sizes and host material compositions are used in order to optimize the device operation. Thisexcitonic optical switching can be established within well defined temperature and magnetic compositionranges. We are proposing amethod for the implementation of this optical device that can be switchedbetween twowell-defined regimes.

Quantum interference patterns predicted by theory due to the finite structure of neutral excitons in InAs quantum rings are corroborated experimentally in the magneto-photoluminescence spectra of these nanostructures. The effects associated to built in electric fields and to the temperature on these Aharonov-Bohm-like oscillations are described and confirmed by complementary experimental procedures.

o gerenciamento de riscos em programas de aventura será analisado de maneira sistemática neste trabalho. Os elementos que conformam os padrões de precaução em atividades comerciais de aventura serão tratados de forma crítica. V árias questões relacionadas à polêmica do credenciamento e certificação de programas comerciais de aventura serão analisadas. Os principais conceitos relativos à segurança na concepção, no planejamento, no monitoramento e na execução de programas turísticos de aventura e eventos na natureza serão abordados. Após a revisão conceitual, será exposto o resultado do estudo dos elementos de gerenciamento de riscos, introduzidos na legislação que rege a implementação da política de desenvolvimento do turismo sustentável no Município de Brotas. Risk management in adventure programs has been systematically analyzed within this work. The elements that integrate the standards of care in commercial adventure programming have been critically approached. Different questions related to the debate on accreditation and certification of adventure programs. The main concepts regarding safety during the conception, planning, monitoring, and execution of adventure tourism programs and events in the wild have been also approached. Following this conceptual revision, the result of the study of risk management topics introduced in the legislation related to the policy of sustainable tourism development in Brotas borough will be displayed.