We propose a controlled experiment to clarify the physical mechanism causing phase lapses of the amplitude for electron transmission through nanoscale devices. Such lapses are generically observed in valleys between adjacent Coulomb--blockade peaks. The experiment involves two quantum dots embedded in the same arm of an Aharonov--Bohm interferometer. It offers a decisive test of "population switching", one of the leading contenders for an explanation of the phenomenon.
We investigate phase coherent electronic transport in an open quantum system, which consists of quantum dots side-coupled to a nanowire. It is demonstrated that coherent switching can be characterized by adjusting the electronic energy. A comparative analysis of quantum coherence effects in side-coupled quantum-dot systems is presented. Our results demonstrate the relevance of electronic nanodevices based on coherent switching by appropriately detuning the side-coupled quantum dots that are located at variable distance along a wire.
The spin-orbit coupling influences the total spin of semiconductor quantum dots. We analyze the theoretical prediction for the combined effects of spin-orbit coupling, weak vertical magnetic fields and deformation of the dot. Our results allow the characterization of the quantum dots as spin switches, controllable with electric gates.
We study the nonequilibrium spin current through a quantum dot consisting of two localized spin-1/2 coupled to two ferromagnetic insulators. The influence of an intra-dot magnetic field and exchange coupling, different dot-reservoir coupling configurations, and the influence of magnon chemical potential differences vs. magnetic field gradients onto the spin current are examined. We discuss various spin switching mechanisms and find that, in contrast to electronic transport, the spin current is very sensitive to the specific coupling configuration and band edges. In particular, we identify 1- a…
Employing oval shaped quantum billiards connected by quantum wires as the building blocks of a linear quantum dot array, we calculate the ballistic magnetoconductance in the linear response regime. Optimizing the geometry of the billiards, we aim at a maximal finite- over zero-field ratio of the magnetoconductance. This switching effect arises from a relative phase change of scattering states in the oval quantum dot through the applied magnetic field, which lifts a suppression of the transmission characteristic for a certain range of geometry parameters. It is shown that a sustainable switchin…
We present magnetoresistance (MR) experiments on an InAs nanowire quantum dot device with two ferromagnetic sidegates (FSGs) in a split-gate geometry. The wire segment can be electrically tuned to a single dot or to a double dot regime using the FSGs and a backgate. In both regimes we find a strong MR and a sharp MR switching of up to 25\% at the field at which the magnetizations of the FSGs are inverted by the external field. The sign and amplitude of the MR and the MR switching can both be tuned electrically by the FSGs. In a double dot regime close to pinch-off we find {\it two} sharp trans…
We investigated the tunneling current peculiarities in the system of two coupled by means of the external field quantum dots (QDs) weakly connected to the electrodes in the presence of Coulomb correlations. It was found that tuning of the external field frequency induces fast multiple tunneling current switching and leads to the negative tunneling conductivity. Special role of multi-electrons states was demonstrated. Moreover we revealed conditions for bistable behavior of the tunneling current in the coupled QDs with Coulomb correlations.
Computational studies based on 6 band k$\cdot$p theory are employed on lens-shaped III-nitride quantum dots (QDs) with focus on the polarization properties of the optical interband transitions. The results predict pronounced linear polarization of the ground-state related transitions for asymmetric QDs of a material with small split-off energy. It is demonstrated that a moderate externally applied electric field can be used to induce a linear polarization and to control its direction. InN is found to be the most efficient choice for dynamic polarization switching controlled by an electric fiel…
We explore the chiral transmission of electrons across graphene heterojunctions for electronic switching using gate geometry alone. A sequence of gates is used to collimate and orthogonalize the chiral transmission lobes across multiple junctions, resulting in negligible overall current. The resistance of the device is enhanced by several orders of magnitude by biasing the gates into the bipolar $npn$ doping regime, as the ON state in the near homogeneous $nn^-n$ regime remains highly conductive. The mobility is preserved because the switching involves a transmission gap instead of a structura…
Quantum capacitance and parity switching of a quantum-dot-based Kitaev chain
Tsung-Dao Lee Institute, Shanghai Jiao Tong University（李政道研究所，上海交通大学）；School of Physics and Astronomy, Shanghai Jiao Tong University（物理与天文学院，上海交通大学）；State Key Laboratory of Micro and Nano Engineering Science, Shanghai Jiao Tong University（微纳工程科学国家重点实验室，上海交通大学）
The charge transport properties of zero-temperature multi-orbital quantum dot systems with one dot coupled to leads and the other dots coupled only capacitatively are studied within density functional theory. It is shown that the setup is equivalent to an effective single impurity Anderson model. This allows to understand the level occupation switching effect as transitions between ground states of different integer occupations in the uncoupled dots. Level occupation switching is very sensitive to small energy differences and therefore also to the details of the parametrized exchange-correlati…
Few-electron systems confined in a quantum dot laterally coupled to a surrounding quantum ring in the presence of an external magnetic field are studied by exact diagonalization. The distribution of electrons between the dot and the ring is influenced by the relative strength of the dot and ring confinement, the gate voltage and the magnetic field which induces transitions of electrons between the two parts of the system. These transitions are accompanied by changes in the periodicity of the Aharonov-Bohm oscillations of the ground-state angular momentum. The singlet-triplet splitting for a tw…
We explore theoretically the spin transport in nanostructures consisting of a gold quantum dot bridging nonmagnetic electrodes and two Mn12-Ph single molecule magnets (SMMs) that are thiol-bonded to the dot but are not in direct contact with the electrodes. We find that reversal of the magnetic moment of either SMM by the application of a magnetic field leads to a large change in the resistance of the dot, i.e., a strong spin valve effect. We show that this phenomenon arises from a novel physical principle: The spin-dependent molecular orbitals that extend over the dot and both SMMs change dra…
We propose a nanoscale device consisting of a double quantum dot with strong intra- and inter- dot Coulomb repulsions. In this design, the current can only flow through the lower dot, but is triggered by the gate-controlled occupancy of the upper dot. At low temperatures, our calculations predict the double dot to pass through a narrow Kondo regime, resulting in highly sensitive switching characteristics between three well-defined states : insulating, normal conduction and resonant conduction.
Recent experiment [Sigrist et al., Phys. Rev. Lett. {\bf 98}, 036805 (2007)] reported switches between 0 and $π$ in the phase of Aharonov-Bohm oscillations of the two-terminal differential conductance through a two-dot ring with increasing voltage bias. Using a simple model, where one of the dots contains multiple interacting levels, these findings are explained as a result of transport through the interferometer being dominated at different biases by quantum dot levels of different "parity" (i.e. the sign of the overlap integral between the dot state and the states in the leads). The redistri…
Strong correlation effects on electron transport through a spinless quantum dot are considered. When two single-particle levels in the quantum dot are degenerate, a conserved pseudospin degree of freedom appears for general tunneling matrix elements between the quantum dot and leads. Local fluctuations of the pseudospin in the quantum dot give rise to a pair of asymmetric conductance peaks near the center of a Coulomb valley. An exact relation to the population switching is provided.
Switching of a single plasmon interacting with equally spaced quantum dots coupled to one-dimensional surface plasmonic waveguide is investigated theoretically via the real-space approach. We showed that the transmission and reflection of a single plasmon can be switched on or off by dynamically tuning and changing the number of the equal transition frequencies of the quantum dots.
The electron wave function experiences a phase modification at coherent transmission through a quantum dot. This transmission phase undergoes a characteristic shift of $π$ when scanning through a Coulomb-blockade resonance. Between successive resonances either a transmission phase lapse of $π$ or a phase plateau is theoretically expected to occur depending on the parity of the corresponding quantum dot states. Despite considerable experimental effort, this transmission phase behaviour has remained elusive for a large quantum dot. Here we report on transmission phase measurements across such a …
We determine the spin exchange coupling J between two electrons located in two vertically tunnel-coupled quantum dots, and its variation when magnetic (B) and electric (E) fields (both in-plane and perpendicular) are applied. We predict a strong decrease of J as the in-plane B field is increased, mainly due to orbital compression. Combined with the Zeeman splitting, this leads to a singlet-triplet crossing, which can be observed as a pronounced jump in the magnetization at in-plane fields of a few Tesla, and perpendicular fields of the order of 10 Tesla for typical self-assembled dots. We use …
A whole series of complementary studies have been performed on the same, single nanowire containing a quantum dot: cathodoluminescence spectroscopy and imaging, micro-photoluminescence spectroscopy under magnetic field and as a function of temperature, and energy-dispersive X-ray spectrometry and imaging. The ZnTe nanowire was deposited on a Si 3 N 4 membrane with Ti/Al patterns. The complete set of data shows that the CdTe quantum dot features the heavy-hole state as a ground state, although the compressive mismatch strain promotes a light-hole ground state as soon as the aspect ratio is larg…
We use the Aharonov-Bohm effect in a four-terminal ring based on a Ga[Al]As heterostructure for the measurement of the relative transmission phase. In each of the two interfering paths we induce a quantum dot. The number of electrons in the two dots can be controlled independently. The transmission phase is measured as electrons are added to or taken away from the individual quantum dots.
Devices for nano- and molecular size electronics are currently a focus of research aimed at an efficient current rectification and switching. Current switching due to conformational changes in the molecules is slow, on the order of a few kHz. Fast switching on the order of 1 THz may be achieved, at least in principle, in a degenerate molecular quantum dot with strong coupling of electrons with vibrational excitations. We show that the mean-field approach fails to properly describe intrinsic molecular switching and present an exact solution to the problem.
We develop a theory for spin transport and magnetization dynamics in a quantum-dot spin valve, i.e., two magnetic reservoirs coupled to a quantum dot. Our theory is able to take into account effects of strong correlations. We demonstrate that, as a result of these strong correlations, the dot gate voltage enables control over the current-induced torques on the magnets, and, in particular, enables voltage-controlled magnetic switching. The electrical resistance of the structure can be used to read out the magnetic state. Our model may be realized by a number of experimental systems, including m…
Recent experiments have demonstrated a working cell suitable for implementing the Quantum-dot Cellular Automata (QCA) paradigm. These experiments have been performed using metal island clusters. The most promising approach to QCA operation involves quasi-adiabatically switching the cells. This has been analyzed extensively in gated semiconductor cells. Here we present a metal island cell structure that makes quasi-adiabatic switching possible. We show how this permits quasi-adiabatic clocking, and enables a pipelined architecture.
The physics of low subthreshold devices is interpreted in terms of a gate dependent change in their mode averaged transmission function, in addition to a capacitive shift in their overall mode spectrum. Accordingly, we explore a variety of subthermal switches that alter the bandwidth, bandgap or amplitude of the transmission, and combinations thereof. The Landauer theory for current flow provides a convenient way to derive the subthreshold swing in each case analytically and suggests ways to beat the Boltzmann limit.
We consider two modifications of a recently proposed three-terminal quantum dot heat engine. First, we investigate the necessity of the thermalization assumption, namely that electrons are always thermalized by inelastic processes when traveling across the cavity where the heat is supplied. Second, we analyze various arrangements of tunneling-coupled quantum dots in order to implement a transmission function that is superior to the Lorentzian transmission function of a single quantum dot. We show that the maximum power of the heat engine can be improved by about a factor of two, even for a sma…
We discuss the behavior of a two-level system coupled to a quantum dot contacted by superconducting source/drain electrodes, representing a simple model for the conformational degree of freedom of a molecular dot or a break junction. The Josephson current is shown to induce conformational changes, including a complete reversal. For small bias voltage, periodic conformational motions induced by Landau-Zener transitions between Andreev states are predicted.
We investigate the Coulomb blockade resonances and the phase of the transmission amplitude of a deformed ballistic quantum dot weakly coupled to leads. We show that preferred single--particle levels exist which stay close to the Fermi energy for a wide range of values of the gate voltage. These states give rise to sequences of Coulomb blockade resonances with correlated peak heights and transmission phases. The correlation of the peak heights becomes stronger with increasing temperature. The phase of the transmission amplitude shows lapses by $π$ between the resonances. Implications for recent…
We study theoretically the transmission through a quantum dot molecule embedded in the arms of an Aharonov-Bohm four quantum dot ring threaded by a magnetic flux. The tunable molecular coupling provides a transmission pathway between the interferometer arms in addition to those along the arms. From a decomposition of the transmission in terms of contributions from paths, we show that antiresonances in the transmission arise from the interference of the self-energy along different paths and that application of a magnetic flux can produce the suppression of such antiresonances. The occurrence of…
The optically induced spin dynamics of a single Mn atom embedded into a single semiconductor quantum dot can be strongly influenced by using the optical Stark effect. The exchange interaction gives rise to simultaneous spin flips between the quantum dot electron and Mn. In the time domain these flips correspond to exchange induced Rabi oscillations, which are typically off-resonant. By applying a detuned laser pulse, the states involved in the flipping can be brought into resonance by means of the optical Stark effect increasing the amplitude of the Rabi oscillations to one. In this paper we s…
The strong sensitivity of the transmission phase through a quantum dot embedded into one arm of a two-wave Aharonov-Bohm interferometer to the Kondo effect is explained. The enhancement takes place because of the buildup of the exchange scattering on the dot due to Kondo correlations even much above $T_{K}$. The enhanced exchange competes with the potential scattering, which is always weak. Both cases of the Anderson impurity model and a multilevel quantum dot are considered. In the latter case in addition to the description of peculiar phase behavior a mechanism leading to ferromagnetic Kondo…
We study the phase of the transmission amplitude through a disordered quantum dot in the Coulomb blockade regime. We calculate the phase dependence on gate voltage for a disorder configuration. We show that over a ``period'', consisting of a resonance and a transmission valley, the total phase change is 0 (mod $2π$). Deviations from this sum rule are small in the parameter (level spacing/charging energy). The disorder-averaged phase-phase correlation function is found showing interaction-induced correlations between phases at different gate voltages.
We study electron transport through a normal lead-quantum dot-topological superconductor-quantum dot-normal lead (N-QD-TS-QD-N) junction. Due to the non-local nature of Majorana fermions (MFs) in the topological superconductor, there are two types of single electron transport processes in the junction: crossed Andreev reflection (CAR) and electron teleportation (ET). When the coupling energy of MFs is much larger than the coupling between MFs and QDs, electron can tunnel through topological superconductor either via CAR or ET depending on the energy levels of QDs. For instance, when both energ…
A broad and a narrow level of a quantum dot connected to two external leads may swap their respective occupancies as a function of an external gate voltage. By mapping this problem onto a multi-flavored Coulomb-gas we show that such population switching is not abrupt. However, trying to measure it by adding a third electrostatically coupled lead may render this switching an abrupt first order quantum phase transition. This is related to the interplay of the Mahan mechanism versus the Anderson orthogonality catastrophe, in similitude to the Fermi edge singularity. A concrete setup for experimen…
We show that the Coulomb blockade in parallel dots pierced by magnetic flux $Φ$ completely blocks the resonant current for any value of $Φ$ except for integer multiples of the flux quantum $Φ_0$. This non-analytic (switching) dependence of the current on $Φ$ arises only when the dot states that carry the current are of the same energy. The time needed to reach the steady state, however, diverges when $Φ\to nΦ_0$.
We explore the quantum transmission through open oval shaped quantum dots. The transmission spectra show periodic resonances and, depending on the geometry parameter, a strong suppression of the transmission for low energies. Applying a weak perpendicular magnetic field changes this situation drastically and introduces a large conductance. We identify the underlying mechanisms being partially due to the specific shape of the oval that causes a systematic decoupling of a substantial number of states from the leads. Importantly a pairwise destructive interference of the transmitting states is en…
Thermoelectric power due to coherent electron transmission through a quantum dot is theoretically studied. In addition to the known features related to resonant peaks, we show that a novel significant structure appears between the peaks. This structure arises from the so-called transmission zero, which is characteristic of coherent transmission through several quantum levels. Because of sensitivity to phase-breaking effect in quantum dots, this novel structure indicates degree of coherency in the electron transmission.
Quantum computing and quantum communication are remarkable examples of new information processing technologies that arise from the coherent manipulation of spins in nanostructures. We review our theoretical proposal for using electron spins in quantum-confined nanostructures as qubits. We present single- and two-qubit gate mechanisms in laterally as well as vertically coupled quantum dots and discuss the possibility to couple spins in quantum dots via exchange or superexchange. In addition, we propose a new stationary wave switch, which allows to perform quantum operations with quantum dots or…
The Aharonov-Bohm effect is measured in a four-terminal open ring geometry based on a Ga[Al]As heterostructure. Two quantum dots are embedded in the structure, one in each of the two interfering paths. The number of electrons in the two dots can be controlled independently. The transmission phase is measured as electrons are added to or taken away from the individual quantum dots. Although the measured phase shifts are in qualitative agreement with theoretical predictions, the phase evolution exhibits unexpected dependence on the magnetic field. For example, phase lapses are found only in cert…
The influence of electron-phonon interaction on the transmission phase shift of an electron passing through a quantum dot is investigated by using the scattering theory. The transmission phase versus the intra-dot level shows a serial of phonon-induced dips. These dips are highly sensitive to electron-phonon interaction strength $λ$, and they are much more pronounced than phonon-assisted sub-peaks appeared in the conductance. Phonon-induce dephasing is also studied, and the results show that the dephasing probability $T_d$ monotonically increases with the electron-phonon interaction strength $…
We optically probe the spectrum of ground and excited state transitions of an individual, electrically tunable self-assembled quantum dot molecule. Photocurrent absorption measurements show that the spatially direct neutral exciton transitions in the upper and lower dots are energetically separated by only ~2 meV. Excited state transitions ~8-16 meV to higher energy exhibit pronounced anticrossings as the electric field is tuned due to the formation of hybridized electron states. We show that the observed excited state transitions occur between these hybridized electronic states and different …
Detecting the transmission phase of a quantum dot via interferometry can reveal the symmetry of the orbitals and details of electron transport. Crucially, interferometry will enable the read-out of topological qubits based on one-dimensional nanowires. However, measuring the transmission phase of a quantum dot in a nanowire has not yet been established. Here, we exploit recent breakthroughs in the growth of one-dimensional networks and demonstrate interferometric read-out in a nanowire-based architecture. In our two-path interferometer, we define a quantum dot in one branch and use the other p…
We theoretically explore optical bistability for possible signature of all optical switching and their performance in a hybrid quantum optomechanical system comprising of two semiconductor microcavity coupled optically. One of the cavity is driven by an external optical pump laser while the second cavity which contains a quantum dot is indirectly driven by light transmitted from the first cavity. The generated bistable behavior due to optomechanical nonlinearity shows a typical optical switching behavior and it can be controlled by changing the laser power, QD cavity coupling, rocking paramete…
We report on the phase measurements on a quantum dot containing a single electron in the Kondo regime. Transport takes place through a single orbital state. Although the conductance is far from the unitary limit, we measure for the first time, a transmission phase as theoretically predicted of π/2. As the dot's coupling to the leads is decreased, with the dot entering the Coulomb blockade regime, the phase reaches a value of π. Temperature shows little effect on the phase behaviour in the range 30--600 mK, even though both the two-terminal conductance and amplitude of the Aharonov-Bohm oscilla…
We perform transmission spectroscopy on single quantum dots and examine the effects of a resident carriers spin, the incident laser spot size, polarization, and power on the experimental contrast. We demonstrate a factor of 4 improvement in the maximum contrast by using a solid immersion lens to decrease the spot area. This increase yields a maximum signal to noise ratio of 2000 Hz-1/2, which will allow for MHz detection frequencies. We anticipate that this improvement will allow further investigation of spectral fluctuation and open up the feasibility for an all-optical read-out of an electro…
We investigate an electronic Mach-Zehnder interferometer with high visibility in the quantum Hall regime. The superposition of the electrostatic potentials from a quantum point contact (QPC) and the residual disorder potential from doping impurities frequently results in the formation of inadvertent quantum dots (QD) in one arm of the interferometer. This gives rise to resonances in the QPC transmission characteristics. While crossing the QD resonance in energy, the interferometer gains a phase shift of $π$ in the interference pattern.
Radio-frequency (rf)- operated single-electron transistors (SETs) are high-sensitivity, fast-response electrometers, which are valuable for developing new insights into single-charge dynamics. We investigate high-frequency (up to 1 MHz) charge noise in an AlGaAs/GaAs quantum dot using a transmission-type rf-SET technique. The electron capture and emission kinetics on a trap in the vicinity of the quantum dot are dominated by a Poisson process. The maximum bandwidth for measuring single trapping events is about 1 MHz, which is the same as that required for observing single-electron tunneling os…
Quantum oscillations of the spin conductance through regular and chaotic 2D quantum dots under the varying Rashba spin orbit interaction and at zero magnetic field have been numerically calculated by summing up the spin evolution matrices for classical transmitting trajectories. Fourier analysis of these oscillations showed power spectra strongly dependent on the dot geometry. For narrow rings the spectra are dominated by a single peak in accordance with previous analytic results. In other geometries the spectra are represented by multiple peaks for regular QD and quasicontinuum for chaotic QD…
Measurement of the transmission phase through a quantum dot (QD) embedded in an arm of a two-terminal Aharonov-Bohm (AB) interferometer is inhibited by phase symmetry, i.e. the property that the linear response conductance of a two-terminal device is an even function of magnetic field. It is demonstrated that in a setup consisting of an interferometer with a QD in each of its arms, with one of the QDs capacitively coupled to a nearby quantum point contact (QPC), phase symmetry is broken when a finite voltage bias is applied to the QPC. The transmission phase via the uncoupled QD can then be de…
We calculated the weak localization correction to the density of the transmission eigenvalues in the case of chaotic quantum dots in the framework of Random Matrix Theory including the parametric dependence on the magnetic field and spin-orbit coupling. The result is interpreted in terms of spin singlet and triplet Cooperon modes of conventional diagrammatic perturbation theory. As simple applications, we obtained the weak localization correction to the conductance, the shot noise power and the third cumulant of the distribution of the transmitted charge.
Recent novel mesoscopic two-arm experiments involving quantum dots, electron interferometry and Aharononov-Bohm effects have enabled measuring the electron transmission probabilities and the phases. Unexpected features in the phases as function of the gap voltage U have simulated intensive theoretical works. It is shown in this paper that the phases (f) and conductances (|C|), appearing in both the experimental and the theoretical works, are interrelated through integral expressions, causing f and log(|C|) to be Hilbert transforms. The empirically found interrelations imply remarkable analytic…
We consider a transport setup containing a double-dot connected by a continuum. Via an exact solution of the time-dependent Schrödinger equation, we demonstrate a highly non-Markovian quantum-coherence-mediated transport through this dot-continuum-dot (DCD) system, which is in contrast with the common premise since in typical case a quantum particle does not reenter the system of interest once it irreversibly decayed into a continuum (such as the spontaneous emission of a photon). We also find that this DCD system supports an unusual steady state with unequal source and drain currents, owing t…
The influence of electron-electron (e-e) interactions on the transmission through a quantum dot is investigated numerically for the Coulomb blockade regime. For vanishing magnetic fields, the conductance peak height statistics is found to be independent of the interactions strength. It is identical to the statistics predicted by constant interaction single electron random matrix theory and agrees well with recent experiments. However, in contrast to these random matrix theories, our calculations reproduces the reduced sensitivity to magnetic flux observed in many experiments. The relevant phys…
We investigate coupling of localized spins in a semiconductor quantum dot embedded in a microcavity with a finite quality factor. The lowest cavity mode and the quantum dot exciton are coupled forming a polariton, whereas excitons interact with localized spins via exchange. The finite quality of the cavity Q is incorporated in the model Hamiltonian by adding an imaginary part to the photon frequency. The Hamiltonian, which treats photons, spins and excitons quantum mechanically, is solved exactly. Results for a single polariton clearly demonstrate the existence of a resonance, sharper as the t…
We report a thermally activated metastability in a GaAs double quantum dot exhibiting real-time charge switching in diamond shaped regions of the charge stability diagram. Accidental charge traps and sensor back action are excluded as the origin of the switching. We present an extension of the canonical double dot theory based on an intrinsic, thermal electron exchange process through the reservoirs, giving excellent agreement with the experiment. The electron spin is randomized by the exchange process, thus facilitating fast, gate-controlled spin initialization. At the same time, this process…
We study the transport through evanescent waves in graphene quantum dots of different geometries. The transmission is suppressed when the leads are attached to edges of the same majority sublattice. Otherwise, the transmission depends exponentially on the distance between leads in rectangular dots, and as a power law in circular dots. The transmission through junctions where the transmitted and reflected currents belong to the opposite valley as the incoming one depends on details of the lattice structure at distances comparable to the atomic spacing.
We study the ballistic edge-channel transport in quantum wires with a magnetic quantum dot, which is formed by two different magnetic fields B^* and B_0 inside and outside the dot, respectively. We find that the electron states located near the dot and the scattering of edge channels by the dot strongly depend on whether B^* is parallel or antiparallel to B_0. For parallel fields, two-terminal conductance as a function of channel energy is quantized except for resonances, while, for antiparallel fields, it is not quantized and all channels can be completely reflected in some energy ranges. All…
We report on growth and characterization of individual InAsP/GaInP quantum dots with variable nominal As molar fraction. Magneto-photoluminescence experiments reveal QD emission in a wide range from 1.3 to 1.8 eV confirming incorporation of As into quantum dots. Transmission electron microscopy reveals a core-cap structure of InAsP quantum dots with an InAs-rich core capped by an InP-rich layer. Inside the core, an As molar fraction up to x=0.12 is observed. The heavy hole g-factor is found to be strongly dependent on As molar fraction, while the electron g-factor is close to the InP values. T…
A pioneering experiment [E. Schuster, E. Buks, M. Heiblum, D. Mahalu, V. Umansky, and Hadas Shtrikman, Nature 385, 417 (1997)] reported the measurement of the transmission phase of an electron traversing a quantum dot and found the intriguing feature of a sudden phase drop in the conductance valleys. Based on the Friedel sum rule for a spinless effective one-dimensional system, it has been previously argued [H.-W. Lee, Phys. Rev. Lett. 82, 2358 (1999)] that the sudden phase drop should be accompanied by the vanishing of the transmission amplitude, or transmission zero. Here we address roles of…
We use a microwave cavity to investigate the influence of a movable absorbing center on the wave function of an open quantum dot. Our study shows that the absorber acts as a position-selective probe, which may be used to suppress those wave function states that exhibit an enhancement of their probability density near the region where the impurity is located. For an experimental probe of this wave function selection, we develop a technique that we refer to as scanning Fourier spectroscopy, which allows us to identify, and map out, the structure of the classical trajectories that are important f…
