Violation of Onsager symmetry for a ballistic channel Coulomb coupled to a quantum ring

We investigate a scattering of electron which is injected individually into an empty ballistic channel containing a cavity that is Coulomb coupled to a quantum ring charged with a single-electron. We solve the time-dependent Schr\"odinger equation for the electron pair with an exact account for the electron-electron correlation. Absorption of energy and angular momentum by the quantum ring is not an even function of the external magnetic field. As a consequence we find that the electron backscattering probability is asymmetric in the magnetic field and thus violates Onsager symmetry.Comment: submitted to EP

Magnetic forces and localized resonances in electron transfer through quantum rings

We study the current flow through semiconductor quantum rings. In high magnetic field the current is usually injected to the arm of the ring preferred by classical magnetic forces. However, for narrow magnetic field intervals that appear periodically on the magnetic field scale the current is injected to the other arm of the ring. We indicate that the appearance of the anomalous -- non-classical -- current circulation results from Fano interference involving localized resonant states. The identification of the Fano interference is based on the comparison of the solution of the scattering problem with the results of the stabilization method. The latter employs the bound-state type calculations and allows to extract both the energy of metastable states localized within the ring and the width of resonances by analysis of the energy spectrum of a finite size system in function of its length. The Fano resonances involving states of anomalous current circulation become extremely narrow on both magnetic field and energy scales. This is consistent with the orientation of the Lorentz force that tends to keep the electron within the ring and thus increases the lifetime of the electron localization within the ring. Absence of periodic Fano resonances in electron transfer probability through a quantum ring containing an elastic scatterer is also explained.Comment: This paper explains the origins of anomalous (non-classical) current circulation reported in http://arxiv.org/abs/1004.219

Electron transfer through a multiterminal quantum ring: magnetic forces and elastic scattering effects

We study electron transport through a semiconductor quantum ring with one input and two output terminals for an elastic scatterer present within one of the arms of the ring. We demonstrate that the scatterer not only introduces asymmetry in the transport probability to the two output leads but also reduces the visibility of the Aharonov-Bohm conductance oscillations. This reduction occurs in spite of the phase coherence of the elastic scattering and is due to interruption of the electron circulation around the ring by the potential defect. The results are in a qualitative agreement with a recent experiment by Strambini et al. [Phys. Rev. B {\bf 79}, 195443 (2009)]. We also indicate that the magnetic symmetry of the sum of conductance of both the output leads as obtained in the experiment can be understood as resulting from the invariance of backscattering to the input lead with respect to the magnetic field orientation.Comment: submitted to PR

Magnetic-field asymmetry of electron wave packet transmission in bent channels capacitively coupled to a metal gate

We study the electron wave packet moving through a bent channel. We demonstrate that the packet transmission probability becomes an uneven function of the magnetic field when the electron packet is capacitively coupled to a metal plate. The coupling occurs through a non-linear potential which translates a different kinetics of the transport for opposite magnetic field orientations into a different potential felt by the scattered electron

Anomalous Stark Shifts in Single Vertically Coupled Pairs of InGaAs Quantum Dots

Vertically coupled Stranski Krastanow QDs are predicted to exhibit strong tunnelling interactions that lead to the formation of hybridised states. We report the results of investigations into single pairs of coupled QDs in the presence of an electric field that is able to bring individual carrier levels into resonance and to investigate the Stark shift properties of the excitons present. Pronounced changes in the Stark shift behaviour of exciton features are identified and attributed to the significant redistribution of the carrier wavefunctions as resonance between two QDs is achieved. At low electric fields coherent tunnelling between the two QD ground states is identified from the change in sign of the permanent dipole moment and dramatic increase of the electron polarisability, and at higher electric fields a distortion of the Stark shift is attributed to a coherent tunnelling effect between the ground state of the upper QD and the excited state of the lower QD.Comment: Conference paper for QD2004 3 figure

Quantum dot defined in two-dimensional electron gas at n-AlGaAs/GaAs heterojunction: simulation of electrostatic potential and charging properties

We present a self-consistent Schroedinger-Poisson scheme for simulation of electrostatic quantum dots defined in gated two-dimensional electron gas formed at n-AlGaAs/GaAs heterojunction. The computational method is applied to a quantitative description of transport properties studied experimentally by Elzermann et al. [Appl. Phys. Lett. {\bf 84}, 4617 (2004)]. The three-dimensional model describes the electrostatics of the entire device with a quantum dot that changes shape and floats inside a gated region when the applied voltages are varied. Our approach accounts for the metal electrodes of arbitrary geometry and configuration, includes magnetic field applied perpendicular to the growth direction, electron-electron correlation in the confined electron system and its interaction with the electron reservoir surrounding the quantum dot. We calculate the electric field, the space charge distribution as well as energies and wave functions of confined electrons to describe opening of two transport channels between the reservoir and the confined charge puddle. We determine the voltages for charging the dot with up to 4 electrons. The results are in a qualitative and quantitative agreement with the experimental data

Bis(tetra­ethyl­ammonium) bis­(hydrogen l-tartrate) l-tartaric acid monohydrate

In the title compound, 2C8H20N+·2C4H5O6 −·C4H6O6·H2O, the presence of the two tetra­ethyl­ammonium cations is balanced by two hydrogen l-tartrate anions. Also present in the asymmetric unit are a mol­ecule of l-tartaric acid and a water mol­ecule. The various components are linked by O—H⋯O hydrogen bonds. In the crystal, two-dimensional networks are formed via O—H⋯O hydrogen bonds and C—H⋯O inter­actions involving the water mol­ecule, the hydrogen l-tartrate anions and the l-tartaric acid mol­ecules. These layers, which stack along [001], are separated by tetra­ethyl­ammonium cations. The latter are also involved in C—H⋯O inter­actions with the anions and the l-tartaric acid and water mol­ecules participating in the two-dimensional network