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The Rashba effect is spin degeneracy lift originated from spin-orbit coupling under inversion symmetry breaking and has been intensively studied for spintronics applications. However, easily implementable methods and corresponding materials for directional controls of Rashba splitting are still lacking. Here, we propose organic-inorganic hybrid metal halide perovskites as 3D Rashba systems driven by bulk ferroelectricity. In these materials, it is shown that the helical direction of the angular momentum texture in the Rashba band can be controlled by external electric fields via ferroelectric switching. Our tight-binding analysis and first-principles calculations indicate that S = 1/2 and J = 1/2 Rashba bands directly coupled to ferroelectric polarization emerge at the valence and conduction band edges, respectively. The coexistence of two contrasting Rashba bands having different compositions of the spin and orbital angular momentum is a distinctive feature of these materials. With recent experimental evidence for the ferroelectric response, the halide perovskites will be, to our knowledge, the first practical realization of the ferroelectric-coupled Rashba effect, suggesting novel applications to spintronic devices.

Understanding of the electronic structure and the electrical transport properties on the nanoscale becomes increasingly important for the development of the next-generation nanodevices. We have developed a first-principles pseudopotential method to calculate the quantum conductance as well as the self-consistent charge distributions of nanostructures and studied the electronic structure and quantum conductance of carbon nanotubes with impurities or defects. Even if the carbon nanotube is metallic instead of semiconducting, boron and nitrogen atoms create acceptor-like and donor-like states which act as scattering centers for conducting electrons. Various defect geometries such as Stone–Wales defects are considered which give rise to interesting localized states and the corresponding conductance characteristics. These localized states are in resonance with the extended states of the metallic nanotube and form quasi-bound states with broadened energy levels leading to novel conductance behaviors. For semiconducting carbon nanotubes, it is shown that various defects located at the junction of two different tubes can produce both shallow and deep defect levels. Theoretical predictions are closely compared with recent scanning tunneling microscopy and scanning tunneling spectroscopy data.

Silicene is a two-dimensional honeycomb lattice made of silicon atoms, which is considered to be a new Dirac fermion system. Based on first-principles calculations, we examine the possibility of the formation of solitonlike topological domain walls (DWs) in silicene. We show that the DWs between regions of distinct ground states of the buckled geometry should bind electrons when a uniform electric field is applied in the perpendicular direction to the sheet. The topological origin of the electron confinement is demonstrated based on numerical calculations of the valley-specific Hall conductivities, and possible experimental signatures of the quantum valley Hall effects are discussed using simulated scanning tunneling microscopy images. Our results strongly suggest that silicene could be an ideal host for the quantum valley Hall effect, thus providing a pathway to the valleytronics in silicon-based technology.

We perform ab initio pseudopotential calculations for a nanocontact between a metallic carbon nanotube and a copper chain. We find that the on-top position is the most stable geometry of the copper chain on the nanotube and a local energy gap of $\ensuremath{\lesssim}0.1 \mathrm{eV}$ opens as the mirror symmetry of the nanotube is broken by the presence of copper. A weak ionic bonding is formed between the tube and the copper chain and the charge density in the conducting channel around the Fermi level is reduced at the contact region. Therefore, the electronic transport across the contact occurs essentially through the tunneling process. Appearance of such a locally semiconducting property in the intrinsically metallic carbon nanotube may explain the unusual low-temperature current-voltage characteristics exhibiting a huge contact resistance or a quantum dot behavior.

We solve the Green's equation exactly for the armchair-type carbon nanotubes with one π-electron tight-binding Hamiltonian and obtain analytic expressions for the conductance of the nanotube with local perturbations. Our results explicitly show the dependence of the conductance on the Fermi level, the tubular radius, and the strength of the perturbation.

We investigate the roles of the pseudospin and the valley degeneracy in electron scattering at graphene edges. It is found that they are strongly correlated with charge density modulations of short-wavelength oscillations and slowly decaying beat patterns in the electronic density profile. Theoretical analyses using nearest-neighbor tight-binding methods and first-principles density-functional theory calculations agree well with our experimental data from scanning tunneling microscopy. The armchair edge shows almost perfect intervalley scattering with pseudospin invariance regardless of the presence of the hydrogen atom at the edge, whereas the zigzag edge only allows for intravalley scattering with the change in the pseudospin orientation. The effect of structural defects at the graphene edges is also discussed.

We report on low‐temperature electronic transport measurements and Technology Computer Aided Design (TACD) modeling of a silicon metal‐oxide‐semiconductor (MOS) quantum dot, with independent gate control of electron densities in the leads and the quantum dot island. This architecture allows the dot energy levels to be probed without affecting the electron density in the leads and vice versa. Appropriate gate biasing enables the dot occupancy to be reduced to the single‐electron level. Independent gate control of the electron reservoirs also enables discrimination between excited states of the dot and density of states (DOS) modulations in the leads.

Electrically‐driven entangled photon generation is demonstrated for the first time using a single semiconductor quantum dot embedded in a light emitting diode structure. The entanglement fidelity is shown to be of sufficient quality for applications such as quantum key distribution.

We have observed the excitonic wave‐packet motion through spectrally resolved four‐wave mixing measurements in a layered semiconductor GaSe, and demonstrated that the four‐wave mixing spectroscopy is a useful tool to observe the wave‐packet motion. We have found that the wave‐packet motion in a quasi‐two‐dimensional system is explained theoretically by using the configuration coordinate model, where the adiabatic potential curve is shifted due to the exciton‐phonon interaction.

Skyrmion excitations are analyzed in imbalanced bilayer quantum Hall systems based on a microscopic theory. A skymion carries both the spin and pseudospin degrees of freedom. In the presence of the parallel magnetic field, the activation energy increases due to the spin component, while it decreases due to the pseudospoin component by deforming a skyrmion into a bimeron (a pair of merons). We propose an approximate formula for the activation energy in imbalanced systems.

We propose a scheme to couple NV centers in diamond through coplanar waveguide resonators. The central conductor of the resonator is split into several pieces which are coupled strongly with each other via simple capacitive junctions or superconducting Josephson junctions. The NV centers are then put at the junctions. The discontinuity at the junctions induces a large local magnetic field, with which the NV centers are strongly coupled to the circuit resonator. The coupling strength $g$ between the resonator and the NV center is of order of $g/2\pi\sim 1$--$30\unit{MHz}$., Comment: 4 pages; 3 figures; several typos corrected; figure 1 regenerated

We report on the first experimental observation of neutral modes in particle‐hole conjugate fractional quantum Hall states using shot noise measurements. The presence of the neutral modes, in addition to producing excess noise in a quantum point contact (QPC), was seen to affect strongly the charge of the tunneling quasiparticles of the charge mode in the QPC and to increase their apparent temperature. The observation of an upstream neutral mode in the 5/2 state may constitute an added indication of its non‐abelian nature.

We have investigated the exciton spin relaxation in InGaAs/AlAsSb quantum wells by time‐resolved spin‐dependent pump and probe reflectance measurements. The spin relaxation time of 1.38 μm‐electron‐heavy‐hole excitons at 150 K is obtained to be 34–43 ps at an excitation power of 50–80 mW. The observed carrier density dependence and temperature independence of the spin relaxation time indicate that the spin relaxation mechanism is dominated by the Bir‐Aronov‐Pikus process.

We report experimental results of electrical transport properties on superconducting quantum interference device (SQUID) coupled with InAs self‐assembled quantum dot (SAQD) which has a unique structural zero‐dimensionality. We successfully fabricated SAQD‐SQUID with two side gates by means of AFM and e‐beam lithography. The side‐gate controlled supercurrent and π junction transition were demonstrated and such results may provide valuable information for the development of quantum information device by employing InAs SAQD.

The results of a group theoretical analysis of the excitonic fine structure are presented and compared with spectroscopic data on single quantum dots. The spectral features reveal the signatures of a symmetry higher than the crystal symmetry (C-3v). A consistent picture of the fine structure patterns for various exciton complexes is obtained with group theory and the concepts of symmetry elevation and symmetry breaking.

We present different schemes for the realization of charge detectors for nanowire quantum dots. We use a two‐dimensional electron gas as a functional substrate for the nanowires where quantum point contacts can be fabricated using etching techniques and by the deposition of metallic gates. The sample designs ensure perfect alignment of the charge detectors to the quantum dots and offer a strong capacitive coupling of the two systems compared to conventional structures on two‐dimensional electron gases with planar geometry.

The transition of plasmons from propagating to localized state was studied in disordered systems formed in doped GaAs/AlGaAs superlattices (SL) by artificial random potential. The theoretical approach based on representation of the plasmon wave function in a Gaussian form was used to acquire a criterion of plasmon localization.

We investigated the effect of in‐situ thermal annealing on InAs quantum dots (QDs) grown site‐selectively on pre‐patterned GaAs substrates. We compare as grown and annealed samples. A morphological transition is observed where originally two QDs merge into one larger dot.

We have fabricated a quantum dot single electron transistor based on an AlGaAs/GaAs heterostructure without any modulation doping. Our device is very stable from an electronic perspective, with clear Coulomb blockade oscillations, and minimal drift in conductance when the device is set to the midpoint of a Coulomb blockade peak and held at constant gate bias. Bias spectroscopy measurements show typical Coulomb 'diamonds' free of any significant charge fluctuation noise. We also observe excited state transport in our device., 3 pages, 5 figures, ICONN2010 conference paper

Time‐resolved spectroscopy was performed with tunable probe pulses for single and multilayer graphene. The induced absorption was observed for multilayer graphene only near probe energy of 0.6 eV, which was explained by the intersubband carrier transitions from states near Dirac point to upper subband states.

We report on Faraday rotation measurements in the THz regime of a two dimensional electron gas in the magnetic field region of cyclotron resonance. Clear steps at several filling factors in the Faraday rotation as a function of carrier density are interpreted as THz ac quantum Hall plateaus. Unlike the dc case, the steps are not quantized but they do depend on filling factor.

We theoretically examine optical Aharonov‐Bohm (AB) effects on trion and biexciton in the type‐II semiconductor quantum dots. Many‐particle states are calculated numerically by the exact diagonalization method. Two electrons in trion and biexciton are strongly correlated to each other, forming a Wigner molecule. The magnetoluminescence spectra from trion and biexciton change discontinuously as the magnetic flux increases by half of h/e, reflecting the Wigner moleculization.

We study the temperature dependence of electron emission from self‐assembled InAs/GaAs quantum dots. A theoretical treatment for electron thermal and tunneling emissions from quantum dots is performed to achieve the “effective emission rate” according to the experimentally obtained quantities. The dominant emission mechanism is found to vary as the temperature decreases.

The time‐resolved photoluminescence experiment has been used to examine temperature dependent dynamics in the quantum well‐quantum dots tunnel injection structures. The obtained pictures of the photoluminescence kinetics for the reference quantum dots and tunnel injection structures indicate a very different relaxation scenario influenced strongly by the temperature dependent phenomena. We point out the role of the phonon bath which affects the back tunneling and carriers escape processes from the quantum dots in the tunnel injection structures.

An experimental study of graphene nanoconstrictions and dots has been performed. Size scales of the fluctuations within these devices are extracted from transport measurements. These sizes are found to be roughly the same size as the constrictions and dots themselves. © 2011 American Institute of Physics., 30th International Conference on the Physics of Semiconductors, ICPS-30, 25 July 2010 through 30 July 2010, Seoul, Series: AIP Conference Proceedings; no. 1399

Semiconductor quantum dots (QDs) can work as an electronic level spectrometer with very high energy resolution. However the series resistance of QDs is strongly affected by the coupling and the states in “detector” dot, which is inadequate for the spectroscopy of a QD under coherent phenomena such as the quantum interference, the Kondo effect, etc. For the purpose, so called side‐coupled configuration [1], in which QDs are connected in parallel, is desirable. Here we report an experimental trial to detect the Kondo density of states in the side‐coupling detection scheme.

We report the low temperature magnetoresistance properties of an InSb quantum well sub‐micron Hall cross with lateral dimensions of 477 nm and active device dimensions of the order of 340 nm. Ballistic transport anomalies are observed in the low field regime including negative bend resistance. The use of such devices as high spatial resolution low field sensors is addressed.

In the present work the theory of polaron states in the quantum wells, quantum wires and quantum dots is developed with due regard for the interaction of charge particles both with bulk and with interface optical phonons. The polaron binding energies are obtained. For the quantum dot case, the contributions of bulk and interface phonons have commensurable quantities. The interface phonon role is much more important in the quantum wells and wires. The essential strengthening as well as the attenuation of polaron interaction is possible with the different interrelations of the structure and the barrier dielectric properties.

A high degree of spin polarization for the neutral exciton in individual InAs quantum dots, without any external magnetic field applied, is demonstrated. The polarization mechanism is shown to be due to the difference in capture time into the QD for the electrons and holes after photo excitation in the wetting layer. This leads to optical pumping of the QD nuclei by spin polarized electrons and hence suppression of the anisotropic electron—hole exchange interaction.

We have studied the magnetic‐field evolution of the fine structure splitting of the exciton bound to nitrogen (N) pairs in GaAs in the Faraday configuration. With applying the magnetic field, the photoluminescence (PL) spectrum splits into several signals and changes their intensities. The observed magneto‐PL spectra indicate the mixing between the split exciton states having the orthogonal linear polarization components in the zero‐magnetic field, which demonstrates the characteristic Zeeman effects of the anisotropic exciton structure bound to the N pairs.

The process of Si‐Ge heterostructures formation in nanowires (NWs) grown by vapor‐liquid‐solid mechanism was investigated using Monte Carlo simulation. Dependences of catalyst drop composition on temperature, flux intensity and nanowire diameter were obtained. Periodical oscillations of drop composition near mean value were observed. Oscillation results from layer‐by‐layer growth at the drop‐whisker interface and necessity of supersaturation onset to start new layer formation. It was demonstrated that it is impossible to grow atomically abrupt axial heterojunctions via classical vapor‐liquid‐solid mechanism due to gradual change of catalyst drop composition when switching the fluxes. This phenomenon is the main reason of heterojunction blurriness. Junction abruptness was found to be dependent on nanowhisker diameter: in adsorption‐induced growth mode abruptness of heterojunction decreases with diameter and in diffusion‐induced mode it increases.

We present a numerical identification scheme for single photon detection (SPD) using a lateral GaAs Quantum Dot (QD). Trapping and resetting of the photo‐generated single electrons can be sensed by the quantum point contact (QPC) fabricated near the dot. A step‐like increase of the QPC current can be observed after laser pulse irradiation meaning an electron is released from the dot. This increase could only be observed if a photo‐generated electron had been trapped in the dot. We show that our developed scheme successfully identifies SPD and measures computationally the trapping time of the generated electron. This work will allow us to analyze single photon to electron spin conversion in a statistical manner.

We carried out the micro and nanoscale investigation of the electrical properties for Pt/a‐plane n‐type GaN Schottky contacts. Using the thermionic emission (TE) model, the temperature‐dependent barrier height and ideality factor were estimated. A notable deviation from the theoretical value in the Richardson constant indicated the formation of inhomogeneous barrier heights. The thermionic field emission (TFE) model produced better fit to the experimental current‐voltage data than the TE model, which suggested that the tunneling, probably due to the presence of a large number of surface defects, played an important role in the Pt/a‐plane n‐type GaN Schottky contacts. Two‐dimensional current map of the Schottky junctions using conductive atomic force microscopy revealed an inhomogeneous spatial current distribution, which well confirmed the existence of the inhomogeneous barrier in the Schottky diodes.

The electrical properties of the percolating networks of carbon nanotubes were simulated by using the circuit simulator. Near the percolation threshold, the whole electrical characteristics of networks are strongly affected by contacts among nanotubes. The electrical contacts on the representative network of nanotube, carbon nanotube network, were modeled by suitable diode models. The non‐linear voltage‐current (V‐I) characteristics at the lower density of the percolated random network can be well explained.

We report the results of polarization resolved reflectivity experiments in GaAs air‐bridge photonic crystals with L3 cavities. We show that the fundamental L3 cavity mode changes, in a controlled way, from a Lorentzian symmetrical lineshape to an asymmetrical form when the linear polarization of the incident light is rotated in the plane of the crystal. The different lineshapes are well fitted by the Fano asymmetric equation, implying that a Fano resonance is present in the reflectivity. We use the scattering matrix method to model the Fano interference between a localized discrete state (the cavity fundamental mode) and a background of continuum states (the light reflected from the crystal slab in the vicinity of the cavity) with very good agreement with the experimental data.

Comunicación presentada en: Physics of Semiconductors, 30th International Conference on the Physics of Semiconductors (25–30 July 2010, Seoul)., We investigate the nonequilibrium charge response of a mesoscopic interferometer (an Aharonov‐Bohm ring) with an interacting quantum dot inserted in one of its arms. The differential conductance is asymmetric when the applied magnetic field reverses its direction. We relate the origin of this effect to the asymmetric charge susceptibility of the dot, which yields, in the mean‐field approximation of the Anderson Hamiltonian, the nonequilibrium potential of the dot. We find that the charge susceptibility becomes an odd function of the flux for symmetric tunnel couplings and examine its behavior when the temperature is lowered below the Kondo temperature. © 2011 American Institute of Physics, Work supported by the Spanish MICINN under Grant No. FIS2008-00781 and the Conselleria d’Innovació, In- terior i Justicia (Govern de les Illes Balears, Spain).

We use time-resolved photoluminescence and photoluminescence excitation spectroscopy to obtain the valence band parameters of wurtzite InP nanowires. We observe the A, B, and C hole bands for these nanowires and obtain both the crystal field and the spin-orbit energies for wurtzite InP nanowires.

A surface emitting microlaser with a metallic‐coated vertical cavity formed by a silver mirror and a distributed Bragg reflector is presented. A simulated reasonable quality factor above 500 is experimentally confirmed. The substrate‐free device with 14 GaAs/AlGaAs quantum wells shows continuous‐wave lasing at room temperature.

We monitor the near‐infrared (NIR) transmission of a GaAs/AlGaAs multi quantum well while illuminated with intense terahertz (THz) pulses. We present the first clear evidence of the intra‐excitonic Autler‐Townes effect when pumping the 1s‐2p transition of the heavy‐hole exciton. We discuss our findings on the basis of a simplified two‐level model and find good qualitative agreement on resonance up to a Rabi energy of 0.6 times the 1s‐2p transition energy.

We have measured the diffusion thermoelectric power in a two‐dimensional electron gas in a GaAs/AlGaAs heterostructure by employing the current heating technique at a low temperature (T = 40 mK) in the magnetic field range 0

Third‐order nonlinear optical responses in single walled carbon nanotubes (SWNTs) encapsulating C70‐ or C84‐ molecules have been investigated by means of pump‐probe spectroscopy. It is found that the nonlinear optical response due the exciton transition is enhanced for SWNTs encapsulating C84‐molecules. The enhancement mechanism is interpreted in terms of hybridization of C84‐molecular states and SWNT band states.

Conference Name: 30th International Conference on the Physics of Semiconductors, ICPS 2010 Date of Conference: 25-30 July 2010 We present calculations on the transport properties of a double quantum dot (DQD) capacitively coupled to another individually biased dot. The effects of the intradot and interdot Coulomb interaction are included within the random-phase approximation (RPA) implemented in the Keldysh formalism. We show that by increasing the bias on the nearby dot the inelastic Coulomb scattering modifies the current in the double dot. The sign of the current depends on the detuning of the double dot levels and intradot transitions lead to negative differential conductance. The enhancement of the current due to the energy quanta transferred from the strongly biased dot suggests a quantum ratchet or Coulomb drag mechanism. © 2011 American Institute of Physics.

We present a theory for the intersubband optics of a doped semiconductor quantum well including Coulomb ground state correlations of the confined interacting electron gas. We find that the electronic ground state correlations lead to a significant broadening of the intersubband absorption spectrum at low temperatures due to additional scattering channels otherwise prohibited by Pauli blocking. The inclusion of electron‐phonon interaction reduces the impact of the electronic correlations on the absorption line width.

We study the bilayer fractional quantum Hall state (FQHS) in layer‐imbalanced configurations at the total Landau level filling factor ν = 1/3, interpreted as the bilayer ν = 1 integer quantum Hall state (IQHS) of composite fermions. We measure the temperature‐dependent magnetoresistance, from which we derive the activation energy gap Δ. We especially focus on the case with large layer‐imbalanced bilayer ν = 1/3 FQHS under tilted magnetic fields. We find that Δ in the single‐layer limit is almost independent on the in‐plane magnetic field B∥ for several total densities, although Δ is increasing as B∥ increases in the case of the bilayer ν = 1 IQHS.

We investigate a circularly polarized photoluminescence using a gated single GaAs quantum well sample in the fractional quantum Hall effect regime. We have found that the lower energy peak χS− is polarized to σ+ polarization. This result is explained by considering the equilibrium between fractionally charged excitons and a two‐dimensional electron system.

We investigate nonequilibrium transport properties of the orbital Kondo effect in a single quantum dot system with the particle‐hole symmetry by means of the renormalized perturbation theory. The asymptotic forms of current and shot noise is calculated up to the leading order in applied bias voltage. The resulting Fano factor for backward current is described in terms of the universal Wilson ratio for arbitrary strength of the on‐site Coulomb interaction.

Using ab initio methods based on the density functional theory, we study the stability of Mn‐doped GaAs and InAs nanowires as well as their electronic and magnetic properties. The model nanowires were constructed using bulk atomic positions of either zinc‐blende or wurtzite structures along (111) and (0001) crystallographic directions, respectively. The calculations show that in such one‐dimensional structures the distribution of Mn ions as well as their mutual spin alignment depends crucially on the crystallographic structure of the wire.

We have established a quantitative method to evaluate the charge sensing sensitivity using a quantum point contact. From the experimental data of a lateral triple quantum dot, we have obtained potential modulations at the saddle point imposed by an electron in each quantum dot of ∼1 μeV. The estimated screening lengths for each quantum dot showed a clear position dependence probably due to the gate structures.

Trapped carrier dynamics in semiconductor quantum dots (QDs) have been studied using terahertz activated luminescence. This technique enabled us to isolate the luminescence emitted by the trapped carriers from the photoluminescence due to interband excitation. Trapped carriers having long lifetimes ∼250 ns at 8 K were observed. Temperature dependence of the trapped carrier lifetime was measured. Activation energy for the trapped carrier decay rate was found to be close to the intersublevel transition energy of the QDs.

We employ surface acoustic waves to control the transfer of photo‐generated carriers between interconnected quantum wells and wires grown on pre‐patterned (311)A GaAs substrates. The wires are embedded at photo‐lithographically defined positions within (Al,Ga)As/GaAs quantum well. Optical studies on these structures have shown sharp PL lines and antibunched photons with tunable emission energy, revealing the presence of several recombination centers within the wire. The spatial separation of these recombination centers emitting single photons is determined from time‐resolved measurements.