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The spin transport characteristics of a nanowire directional electronic coupler have been evaluated theoretically via a transfer matrix approach. The application of a gate field in the region of mixing allows for control of spin current through the different leads of the coupler via the Rashba spin-orbit interaction. The combination of spin-orbit interaction and applied gate voltages on different legs of the coupler give rise to a controllable modulation of the spin polarization. Both structural factors and field strength tuning lead to a rich phenomenology that could be exploited in spintronic devices., Comment: 9 pages, 4 figures

The authors gratefully acknowledge financial support from the European Union (FPVII (2007-2013) under grant agreement n° 318287 Landauer) as well as the state of Bavaria. The Brazilian authors acknowledge the support of CNPq. V. L.-R. acknowledges the support of FAPESP (grants 2014/02112-3 and 2015/10765-0). We present the realization of four different learning rules with a quantum dot memristor by tuning the shape, the magnitude, the polarity and the timing of voltage pulses. The memristor displays a large maximum to minimum conductance ratio of about 57000 at zero bias voltage. The high and low conductances correspond to different amounts of electrons localized in quantum dots, which can be successively raised or lowered by the timing and shapes of incoming voltage pulses. Modifications of the pulse shapes allow altering the conductance change in dependence on the time difference. Hence, we are able to mimic different learning processes in neural networks with a single device. In addition, the device performance under pulsed excitation is emulated combining the Landauer-Büttiker formalism with a dynamic model for the quantum dot charging, which allows explaining the whole spectrum of learning responses in terms of structural parameters that can be adjusted during fabrication such as gating efficiencies and tunneling rates. The presented memristor may pave the way for future artificial synapses with a stimulus-dependent capability of learning. Postprint

This work aims to investigate the effects of magnetic field strength and direction on the electronic properties and optical response of GaAs/AlGaAs-based heterostructures. An investigation of the excitonic spin-splitting of a disordered multiple quantum well embedded in a wide parabolic quantum well is presented. The results for polarization-resolved photoluminescence show that the magnetic field dependencies of the excitonic spin-splitting and photoluminescence linewidth are crucially sensitive to magnetic field orientation. Our experimental results are in good agreement with the calculated Zeeman splitting obtained by the Luttinger model, which predicts a hybridization of the spin character of states in the valence band under tilted magnetic fields.

We employ the circular-polarization-resolved magnetophotoluminescence technique to probe the spin character of electron and hole states in a GaAs/AlGaAs strongly coupled double-quantum-well system. The photoluminescence (PL) intensities of the lines associated with symmetric and antisymmetric electron states present clear out-of-phase oscillations between integer values of the filling factor $\ensuremath{\nu}$ and are caused by magnetic-field-induced changes in the population of occupied Landau levels near to the Fermi level of the system. Moreover, the degree of circular polarization of these emissions also exhibits the oscillatory behavior with increasing magnetic field. Both quantum oscillations observed in the PL intensities and in the degree of polarizations may be understood in terms of a simple single-particle approach model. The $\mathbf{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{p}$ method was used to calculate the photoluminescence peak energies and the degree of circular polarizations in the double-quantum-well structure as a function of the magnetic field. These calculations prove that the character of valence band states plays an important role in the determination of the degree of circular polarization and, thus, resulting in a magnetic-field-induced change of the polarization sign.

We present a systematic study of lead-salt nanocrystals (NCs) doped with Mn. We have developed a theoretical simulation of electronic and magneto-optical properties by using a multi-band calculation including intrinsic anisotropies and magnetic field effects in the diluted magnetic semiconductor regime. Theoretical findings regarding both broken symmetry and critical phenomena were studied by contrasting two different host materials (PbSe and PbTe) and changing the confinement geometry, dot size, and magnetic doping concentration. We also pointed out the relevance of optical absorption spectra modulated by the magnetic field that characterizes these NCs.

The photoluminescence of annealed Cd\(_x\)Zn\(_{1-x}\)Se quantum dots (QDs) under the influence of an external magnetic field has been studied in this paper. Post-growth annealing was performed for different annealing times. Above a critical annealing time, the QD luminescence shows a pronounced red-shift of the Zeeman split magnetic subcomponents. This observation is in contrast to the blue-shift caused by the diamagnetic behavior that is usually observed in non-magnetic QDs. We attribute our finding to the paramagnetism caused by the mixing of heavy and light hole states. Hence, post-growth thermal annealing treatment might be employed to render undoped epitaxial QDs intrinsically magnetic in a controlled manner. Two theoretical models were developed: a few-particle model to account for excitonic complex effects and a multiband calculation that describes the valence band hybridization. Contrasting the two models allowed us to unambiguously elucidate the nature of such an effect.

This work reports the investigation on the structural differences between InAs quantum rings and their precursor quantum dots species as well as on the presence of piezoelectric fields and asymmetries in these nanostructures. The experimental results show significant reduction in the ring dimensions when the sizes of capped and uncapped ring and dot samples are compared. The iso-lattice parameter mapped by grazing-incidence x-ray diffraction has revealed the lateral extent of strained regions in the buried rings. A comparison between strain and composition of dot and ring structures allows inferring on how the ring formation and its final configuration may affect optical response parameters. Based on the experimental observations, a discussion has been introduced on the effective potential profile to emulate theoretically the ring-shape confinement. The effects of confinement and strain field modulation on electron and hole band structures are simulated by a multiband k.p calculation.

We report a study of magnetic responses of neutral and charged excitons in quantum wells, which are very sensitive to the strong spin hybridization of holes. This effect can be used to engineer the spin character of excitonic complexes in two-dimensional systems tuned by the magnetic field strength. Conditions for spin flip for each kind of excitonic complex is detailed and the nature of the effect discussed. Differences in the effective Zeeman splitting between neutral and charged excitons are theoretically predicted and unambiguously confirmed experimentally. Circularly polarized resolved photoluminescence has been used to study these effects under applied magnetic fields. The intertwining of spin dynamics of excitons and trions is discussed.

L. Villegas-Lelovsky,1 Fanyao Qu,2 L. O. Massa,2 V. Lopez-Richard,3 and G. E. Marques3 1Instituto de Fisica, Universidade Federal de Uberlândia, 38.400-902, Uberlândia, Minas Gerais, Brazil 2Instituto de Fisica, Universidade de Brasilia, Brasilia-DF 70910-900, Brazil 3Departamento de Fisica, Universidade Federal de Sao Carlos, 13.565-905, Sao Carlos, Sao Paulo, Brazil (Received 24 March 2011; revised manuscript received 3 June 2011; published 10 August 2011)

We report a study of dynamic effects detected in the time-resolved emission from quantum dot ensembles. Experimental procedures were developed to search for common behaviors found in quantum dot systems independently of their composition: three quantum dot samples were experimentally characterized. Systems with contrasting interdot coupling are compared and their sensitivity to the excitation energy is analyzed. Our experimental results are compared and contrasted with other results available in literature. The optical recombination time dependence on system parameters is derived and compared to the experimental findings. We discuss the effects of occupation of the ground state in both valence and conduction bands of semiconductor quantum dots in the dynamics of the system relaxation as well as the nonlinear effects.

A method to determine the effects of the geometry and lateral ordering on the electronic properties of an array of one-dimensional self-assembled quantum dots is discussed. A model that takes into account the valence-band anisotropic effective masses and strain effects must be used to describe the behavior of the photoluminescence emission, proposed as a clean tool for the characterization of dot anisotropy and/or inter-dot coupling. Under special growth conditions, such as substrate temperature and Arsenic background, 1D chains of In0.4Ga0.6 As quantum dots were grown by molecular beam epitaxy. Grazing-incidence X-ray diffraction measurements directly evidence the strong strain anisotropy due to the formation of quantum dot chains, probed by polarization-resolved low-temperature photoluminescence. The results are in fair good agreement with the proposed model.

By breaking the spatial symmetry of two coupled quantum dots, we are able to manipulate the $p\text{\ensuremath{-}}d$-exchange interaction between a hole and a single-${\text{Mn}}^{2+}$ ion by means of an external electric field. It is found that the magnetic energy can be tuned in a wide range. Depending on the position of the Mn ion located within the system, effective Zeeman effects induced by the exchange interaction may be switched on/off and even exhibits peak maxima values which accounts for the interdot resonant coupling.

We report a systematic study of magneto-optical properties in CdZnSe/ZnSe semiconductor quantum dots QDs subjected to postgrowth thermal annealing. The theoretical and experimental characterizations are combined in order to understand the evolution of Zeeman splitting and the blueshift as well as redshift of the magnetic subcomponents with magnetic field strength of excitons confined in annealed QDs as a function of different annealing times. A combination of a multiband model as well as parameter interpolation supported by ab initio calculations is presented and points toward an inversion of the light-hole-heavy-hole states due to annealing. The band mixing of exciton states explains besides the variation in the Zeeman splitting for differently annealed QD excitons, the evolution of the diamagnetic blueshift into a paramagnetic redshift of the magnetic subcomponents. A discussion of the effects associated to the Coulomb interaction on the polarized excitonic recombinations modulated by magnetic field is given.

Multilayer In0.4Ga0.6As/GaAs quantum dot (QD) chain samples are investigated by means of cw and time-resolved photoluminescence (PL) spectroscopy in order to study the peculiarities of interdot coupling in such nanostructures. The temperature dependence of the PL has revealed details of the confinement. Non-thermal carrier distribution through in-chain, interdot wave function coupling is found. The peculiar dependences of the PL decay time on the excitation and detection energies are ascribed to the electronic interdot coupling and the long-range coupling through the radiation field. It is shown that the dependence of the PL decay time on the excitation wavelength is a result of the superradiance effect.

We report a comprehensive discussion of quantum interference effects due to the finite structure of neutral excitons in quantum rings and their first experimental corroboration observed in the optical recombinations. The signatures of built-in electric fields and temperature on quantum interference are demonstrated by theoretical models that describe the modulation of the interference pattern and confirmed by complementary experimental procedures.

We examine the effects of the full Dresselhaus spin-orbit coupling on laterally confined quantum wire states. An analysis of the relative contributions due to linear, quadratic, and cubic Dresselhaus spin-orbit terms on the energy levels, spin splitting, and spin polarization has been carried out. The effects of wire cross-sectional geometry shapes on the electronic structure are explored. In particular we compared the results of semicylindrical and cylindrical confinements and have found important differences between the spin degeneracy of the ground-state level and the spin-polarization dependence on sign inversion of the free linear momentum quantum number along the wire axis. Different from other symmetries, in both cases here considered, the stronger spin-splitting effects come from the quadratic Dresselhaus term. We report ideal conditions for realization of spin-field filter devices based on symmetry properties of the spin splitting of the ground state in semicylindrical quantum wires.

C. Trallero-Giner,1 V. Lopez-Richard,2 S. E. Ulloa,3 and G. E. Marques2 1Department of Theoretical Physics, Havana University, Vedado 10400, Havana, Cuba 2Departamento de Fisica, Universidade Federal de Sao Carlos, 13560-905, Sao Carlos, SP, Brazil 3Department of Physics and Astronomy and Nanoscale and Quantum Phenomena Institute, Ohio University, Athens, Ohio 457501-2979, USA Received 17 November 2008; revised manuscript received 6 March 2009; published 3 April 2009

The one phonon Raman scattering efficiency for zincblende-type semiconductors in high magnetic fields has been obtained. Special emphasis has been given to the enhancement of the electronic lifetime broadening due to resonant coupling between different intraband states by the LO-phonons. The sharp resonances obtained by magneto-Raman scattering in GaAs further allow the identification of magnetopolaron effects.

The transport of electrons through a GaAs/AlAs double-barrier structure with $p$-type doped contacts was investigated using time-resolved photoluminescence spectroscopy. Under illumination, the current-voltage characteristics of the device present two additional features attributed, respectively, to resonant $\ensuremath{\Gamma}\text{\ensuremath{-}}\ensuremath{\Gamma}$ and $\ensuremath{\Gamma}\text{\ensuremath{-}}X$ electron tunneling. Optical measurements for biases where these two alternative transport mechanisms have competitive probabilities revealed an unusual carrier dynamics. The quantum well emission is strongly delayed and we observe a remarkable nonlinear effect where the emission intensity decreases at the arrival of a laser pulse. We propose a simple model that adequately describes our results where we assume that the indirect-transition rate depends on the density of electrons accumulated along the structure.

We derive closed analytical expressions for the order parameter $\Phi (x)$ and for the chemical potential $\mu $ of a Bose-Einstein Condensate loaded into a harmonically confined, one dimensional optical lattice, for sufficiently weak, repulsive or attractive interaction, and not too strong laser intensities. Our results are compared with exact numerical calculations in order to map out the range of validity of the perturbative analytical approach. We identify parameter values where the optical lattice compensates the interaction-induced nonlinearity, such that the condensate ground state coincides with a simple, single particle harmonic oscillator wave function.

A negative magnetic dispersion of the degree of circular polarization is reported for the photoluminescence of self-assembled ZnCdSe quantum dots (QDs) after a postgrowth thermal annealing (TA) treatment. Multiband calculations in the framework of the $\mathbf{k}\ensuremath{\cdot}\mathbf{p}$ model reveal that the phenomenon is explicable considering, apart from the changes in the confinement and composition of the QDs due to TA-induced Zn-Cd interdiffusion, the presence of extra charges of one kind within the structure.

We report theoretical studies of the spin splitting caused by inversion asymmetries in quantum ring-shaped self-assembled quantum dots with circular cross sections. We analyze the conduction band and the spinsplitting electronic energy dispersions of the system in the presence of both bulk Dresselhaus and structural Rashba inversion asymmetries as a function of quantum ring geometrical parameters. We have explored the interplay effects between the circular confinement symmetry and the magnitude of the spin-orbit constants for the dot material. We describe universal conditions to operate a spin-field-effect transistor based on quantum rings with identical linear Dresselhaus and Rashba spin-orbit coupling interactions. The results show to be sensitive to both the quantum ring radii and the dot thickness.

Considering the Gross-Pitaevskii integral equation we are able to formally obtain an analytical solution for the order parameter $\Phi (x)$ and for the chemical potential $\mu $ as a function of a unique dimensionless non-linear parameter $\Lambda $. We report solutions for different range of values for the repulsive and the attractive non-linear interactions in the condensate. Also, we study a bright soliton-like variational solution for the order parameter for positive and negative values of $\Lambda $. Introducing an accumulated error function we have performed a quantitative analysis with other well-established methods as: the perturbation theory, the Thomas-Fermi approximation, and the numerical solution. This study gives a very useful result establishing the universal range of the $\Lambda $-values where each solution can be easily implemented. In particular we showed that for $\Lambda, Comment: 8 figures

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 FAPESP (2012/51415-3 and 2012/13052-6), CNPq and CAPES. We have investigated photodetectors based on an AlGaAs/GaAs double barrier structure with a nearby lattice-matched GaInNAs absorption layer. Photons with the telecommunication wavelength λ=1.3 μm lead to hole accumulation close to the double barrier inducing a voltage shift ΔV(V) of the current-voltage curve, which depends strongly on the bias voltage V. A model is proposed describing ΔV(V) and the photocurrent response in excellent agreement with the experimental observations. According to the model, an interplay of the resonant tunneling diode (RTD) quantum efficiency η(V), the lifetime of photogenerated and accumulated charge carriers τ(V), and the RTD current-voltage relation in the dark determines best working parameters of RTD photodetectors. Limitations and voltage dependencies of the photoresponse are discussed. Publisher PDF

We report experimental evidence of excitonic spin-splitting, in addition to the conventional Zeeman effect, produced by a combination of the Rashba spin-orbit interaction, Stark shift and charge screening. The electric-field-induced modulation of the spin-splitting are studied during the charging and discharging processes of p-type GaAs/AlAs double barrier resonant tunneling diodes (RTD) under applied bias and magnetic field. The abrupt changes in the photoluminescence, with the applied bias, provide information of the charge accumulation effects on the device., 4 pages, 2 figures

We have investigated polarization-resolved photoluminescence under applied voltage in $p\text{\ensuremath{-}}i\text{\ensuremath{-}}p$ $\mathrm{Ga}\mathrm{As}∕\mathrm{Al}\mathrm{As}$ double-barrier diodes. We have observed oscillations in the degree of polarization up to 36% at $B=15\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ with sign reversals occurring near to the hole subband resonances. At high voltages a polarization saturation up to 25% at $B=15\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ is observed. The data are interpreted by using simulations based on a simple theoretical model that considers spin conservation for tunneling and the relaxation processes for carriers at Zeeman states in the quantum well. Our work offers the prospect for the development of voltage-controlled spin filtering systems using standard nonmagnetic semiconductor heterostructures.

We present a theoretical study on the effects of electron-LO-phonon interaction in two coupled stacked $\mathrm{In}\mathrm{As}∕\mathrm{In}\mathrm{Al}\mathrm{As}$ quantum dots. The resonant and nonresonant electron-phonon coupling contributions to the polaron states are obtained in the framework of the Green function formalism and perturbation approaches at zero and finite temperatures. Ground state renormalization is achieved due to phonon virtual absorption at $Tg0$. Tunneling effects between dots have been addressed and their influence on the electronic properties and optical absorption are analyzed. Topological modifications of electronic orbitals are found as a result of phonon-assisted tunneling.

We calculate the g-factor for electron, holes, and electron-hole pairs in CdTe quantum dots using the multiband k"p theory. The results show that g-factors are highly sensitive to the spatial confinement and its magnitude as well as sign may change when the geometric shape of the dot is altered. We identify the valence-conduction interband coupling between states with different parities, as mainly responsible for level

Atomic manipulation and scanning tunnel microscope experiments on metal surfaces have shown that electronic states in a ``quantum corral'' can be locally monitored and used to analyze the nonlocal effects of perturbations. We study new corral geometries defined by families of confocal parabolas. General solutions of the Schr\"odinger equation for the interior problem with Dirichlet (hard wall) boundary conditions are found exactly in terms of zeroes of hypergeometric functions. We show that the Hilbert space of solutions is separated in subspaces with odd and even symmetry. We perform numerical evaluation of the zeroes and study the effects of the parabolic curvatures on the eigenvalues and eigenfunctions of the parabolic quantum corral. The evolution of the local density of states with energy as a function of parabolic corral geometry is also analyzed. We find that under suitable conditions, the distribution of state antinodes can be described as directed intensity beams, which could be used as ``quantum beacons'' in future generations of ``quantum mirage'' experiments or optical and acoustic analogs of quantum corrals for the state node distribution.

The effects of the interband coupling on the magnetoplasmons and the single-particle excitations are studied for a two-dimensional electron gas in narrow-gap semiconductor quantum wells. Raman selection rules and scattering configurations for the observation of the spin-flip transitions in the magneto-Raman scattering are achieved. Our results reveal an unambiguous relation between the conduction band structure and the Raman-scattering spectrum in narrow-gap semiconductor quantum wells. The electron cyclotron mass and the effective Lande g factor can be directly determined from the dependence of the magneto-Raman spectrum on the filling factor in the Faraday and the Voigt configurations, respectively.

A theoretical study of optical properties in narrow gap semiconductor quantum wells has been developed using an 8x8 Kane Hamiltonian. The interband transition selection rules have been obtained and a detailed description of the interband absorption using Voight and Faraday scattering configurations has been given. Interesting effects produced by the intraband admixture, such as spin-flip transitions, will be discussed. The complementation of measurements using different scattering configurations will be analyzed.

Detailed experimental and theoretical studies of lateral electron transport in a system of quantum dot chains demonstrate the complicated character of the conductance within the chain structure due to the interaction of conduction channels with different dimensionalities. The one-dimensional character of states in the wetting layer results in an anisotropic mobility, while the presence of the zero-dimensional states of the quantum dots leads to enhanced hopping conductance, which affects the low-temperature mobility and demonstrates an anisotropy in the conductance. These phenomena were probed by considering a one-dimensional model of hopping along with band filling effects. Differences between the model and the experimental results indicate that this system does not obey the simple one-dimensional Mott's law of hopping and deserves further experimental and theoretical considerations.

Transport properties of holes in InP nanowires were calculated considering electron-phonon interaction via deformation potentials, the effect of temperature and strain fields. Using molecular dynamics, we simulate nanowire structures, LO-phonon energy renormalization and lifetime. The valence band ground state changes between light- and heavy-hole character, as the strain fields and the nanowire size are changed. Drastic changes in the mobility arise with the onset of resonance between the LO-phonons and the separation between valence subbands., 4 pages, 4 figures

We have systematically studied the single-particle states in quantum rings produced by a set of concentric circular gates over a graphene sheet placed on a substrate. The resulting potential profiles and the interaction between the graphene layer and the substrate are considered within the Dirac Hamiltonian in the framework of the envelope function approximation. Our simulations allow microscopic mapping of the character of the electron and hole quasi-particle solutions according to the applied voltage. General conditions to control and operate the bound state solutions are described as functions of external and controllable parameters that will determine the optical properties ranging from metallic to semiconductor phases. Contrasting behaviors are obtained when comparing the results for repulsive and attractive voltages as well as for variation of the relative strength of the graphene‐substrate coupling parameter. (Some figures may appear in colour only in the online journal)

We propose a spin-current switch, which is composed of vertical asymmetric double quantum dots (DQD) containing single manganese, and subjected to an electric field along the growth direction. We demonstrate electrical tunability of charge and spin dependent interdot quantum couplings between two dots. Manipulation of individual Mn2+ spin and electrical control of spin-splitting depend strongly on the magnetic impurity position. By sweeping electrical field, the spin-splitting is reduced from its maximum value to zero for Mn2+ ion located inside one of the quantum dots. For Mn2+ ion inside the other quantum dot, however, the spin-splitting builds up from zero to its maximum value. Hence the spin-splitting may act as a fingerprint of spin- and charge-state of hole in single-Mn doped DQDs, and may also be used as the basis to construct a spin-current switch.

We report on the strong temperature-dependent thermal expansion, D, in CdS quantum dots (QDs) embedded in a glass template. We have performed a systematic study by using the temperature-dependent first-order Raman spectra, in CdS bulk and in dot samples, in order to assess the size dependence of D, and where the role of the compressive strain provoked by the glass host matrix on the dot response is discussed. We report the Gr¨ uneisen mode parameters and the anharmonic coupling constants for small CdS dots with mean radius R 2:0 nm. We found that parameters change, with respect to the bulk CdS, in a range between 20 and 50%, while the anharmonicity contribution from two-phonon decay channel becomes the most important process to the temperature-shift properties. (Some figures may appear in colour only in the online journal)

A pathway to design non-magnetic artificial molecules which display controllable magnetic properties is addressed theoretically by studying the effects of in-plane electrical field, spin–orbit interaction (SOI) and geometrical parameters on the magnetic phase transitions in few-electron lateral double quantum dots (DQDs). We demonstrate the tunability of the magnetic phase diagram of two-electron DQDs as the system is changed from a molecule to an atom, in both weak and strong SOI regimes. We find an unusual jump in the magnetization and an asymmetric peak of the magnetic susceptibility. In addition, both the asymmetric susceptibility peak position and the magnetic phase diagram are strongly dependent on the interdot tunnel coupling, which can be tuned effectively by changing repulsive barrier voltage and/or interdot distance, the number of electrons and the SOI strength. With increasing interdot tunnel-coupling strength, for instance, the rate of paramagnetic-to-diamagnetic phase area increases. The SOI makes the paramagnetic phase more stable under magnetic field. Moreover, the effects of geometry deviation on the electronic structure and magnetic property of the DQD are also discussed.

We investigate theoretically magnetic properties of tunable lateral double quantum dots (DQDs) containing few electrons, subjected to spin-orbit interaction (SOI) and vertical magnetic field, using exact diagonalization (ED) method. To circumvent the cumbersome construction of matrix elements of the Hamiltonian, we adopt the modified Gaussian functions to describe atomic-like orbital states of single quantum dots. The numerical artifacts in the single-electron energy spectrum are avoided by separating the full Hilbert space into two sub-spaces. The interplay of SOI and interdot tunnel coupling leads to an oscillatory behaviour in the magnetization at low temperature. Sweeping interdot barrier voltage and adjusting interdot distance produce not only magnetic phase transition but also switches between atomic and molecular orbitals.

We have studied the polarized emission from the contact layers and the quantum well of asymmetric n-type GaAs/GaAlAs resonant tunneling diodes under high magnetic fields (up to 19 T) parallel to the tunnel current. The photoluminescence from the GaAs contact layers shows evidence of the recombination from a two-dimensional hole gas accumulated next to the GaAlAs barrier and free carriers. Both the energy position and the intensity of this emission are voltage dependent. In addition, the photoluminescence from the two-dimensional hole gas and quantum well is strongly spin-polarized under the applied voltage and high magnetic fields. Pronounced oscillatory features are observed in the magnetic field dependence of the polarization degree from the quantum well and the two-dimensional hole emissions at integer filling factors. The obtained data show that resonant tunneling diodes are interesting systems to study the physical properties of voltage-controlled two-dimensional gases in the accumulation layers and quantum well.

We investigate theoretically the tunability of the effective electron g-factor in lateral double quantum dots, subjected simultaneously to spin-orbit interaction and vertical electrical and magnetic fields. We find that, by sweeping interdot barrier voltage or by changing interdot distance, the character of the electronic states can be modified from atomic-like to molecular-like and vice-versa. We report theoretical predictions for interdot voltage induced giant effective g-factor and study its dependence on the spin-orbit interaction strength. To avoid numerical artifacts in the single-electron energy spectrum, we adopt a set of modified Gaussian functions as basis, divide the full Hilbert space into orthogonal sub-spaces, and use an exact diagonalization method. In order to correct ill-definitions of g-factor found in the literature, we point out an unambiguous way to evaluate it.

We have investigated the polarized-resolved photoluminescence from the contact layers and the quantum-well in an n-type GaAs/GaAlAs resonant tunneling diode for magnetic fields up to 19 T. The optical emission from the GaAs contact layers comprises the recombination from highly spin-polarized two-dimensional electron and hole gases with free tunneling carriers. Both the energy position and intensity of this indirect recombination are voltage-dependent and show remarkably abrupt variations near scattering-assisted tunneling resonances. Our results show that these two dimensional gases act as spin-polarized sources for carriers tunneling through the well in resonant tunneling diodes.

The Stokes shift detected in PbS nanocrystals is analyzed by optical absorption (OA), photoluminescence (PL) and atomic force microscopy (AFM). The samples were synthesized by fusion method over two different glass substrates, and identical size PbS dot structures with radius 4.1 nm grown showed PL and OA peaks separated by 0.15 and 0.10 eV. The origin of these large Stokes shifts are analyzed whether they are attributed to the nonradiative recombination associated to impurity states in prepared doped samples or to radiative transitions between exciton states induced by electron-hole (e-h) exchange Coulomb interaction.

We demonstrate theoretically a pathway for electrical control of magnetic properties of tunable lateral double InAs quantum dots containing two-electrons, subjected to spin-orbit interaction (SOI), vertical electrical and magnetic fields. In the regime of low temperature and weak magnetic field, interplay of interdot tunnel coupling and hybridized magnetoelectric effect induces “s”-like behavior of magnetization and a peak of susceptibility which are very sensitive to interdot barrier voltage (VB) and interdot distance (d). Sweeping VB and adjusting d not only impact magnetic phase transition, but also switch electronic and magnetic properties from atomic to molecular in nature. Furthermore, SOI broadens the magnetic field interval of paramagnetic phase and changes magnitude of magnetization and susceptibility.

We studied magneto-optical properties in CdTe– Cd x Hg (1−x) Te quantum wells as a function of a magnetic field, B 0 , for x close to the semimetal phase ( E g =0 at x c =0.175 ). In these structures the large nonparabolicity, the strong interband mixing and the small effective masses provide a variety of novel optical and electronic properties. We discuss features related to band admixture in different configurations. In principle, the number of allowed transitions, the effects of spin-flip transitions, the odd dependence of oscillator strengths on B 0 and the anisotropic behavior of the absorption for different polarization are complementary tools.

We study effects of spin-orbit coupling and electron-electron correlation, which can be electrically tuned, on the singlet-triplet entanglement in double lateral quantum dots charged with two electrons. We have found that the magnetic character of a double-dot system can be changed from diamagnetic to paramagnetic, only by adjusting the strength of spin-orbit coupling. Coulomb interaction leads to an unusual singlet-triplet energy splitting, accompanied by a shift of this transition energy to the lower magnetic field side in the energy spectrum.

Interdot coupling in (In,Ga)As/GaAs quantum dot arrays is studied by means of steady state and time-resolved photoluminescence (PL). A peculiar dependence of the PL decay time on the excitation and detection energy is revealed and ascribed to the peculiarities of the carrier and energy relaxation caused by both immediate electronic interdot coupling and long-range coupling through the radiation field.

We have investigated the polarized emission from a n-type GaAs∕AlGaAs resonant tunneling diode under magnetic field. The GaAs contact layer emission shows a large constant negative circular polarization. A similar result is observed for the quantum well, but only when electrons are injected from the substrate, while for inverted biases, the polarization tends to become positive for small voltages and large laser excitation intensities. We believe that the quantum well polarization may be associated to the partial thermalization of minority carriers on the well subbands and is thus critically dependent on the bias-controlled density of carriers accumulated in the well.

We propose an optical switch based on a spin tuning mechanism in diluted-magnetic semiconductor quantum dots. At certain critical magnetic field, Bc, the Zeeman spin-splitting energies can cross leading to a zero value of the effective electron g-factor and the Fermi level undergoes a spin-flip transition. Magneto-optical switching is obtained for magnetic fields below and above Bc. Correlations between Bc, confinement shapes, dot sizes, and host material compositions have been established within well-defined temperature and magnetic impurity composition ranges. The generality of the presented theoretical framework allows for its application to magnetic field controlled quantum dot arrays, and spin-injection among others.

A method of characterizing the quantum dot charge buildup in a magnetic field is proposed based on the far-infrared magneto-optical response properties. The inherent topological symmetry of the nanostructure and several optical configurations are analyzed as key factors determining the appropriate use of intraband transitions as a probing tool for the quantum dot charge buildup.