Directed electron transport through a ballistic quantum dot under microwave radiation

Rectification of microwave radiation by asymmetric ballistic dot is studied at different frequencies (1-40 GHz), temperatures, and magnetic fields. Dramatic reduction of the rectification is found in magnetic fields at which the cyclotron radius of electron orbits at the Fermi level is less than the size of the dot. With respect to the magnetic field, both symmetric and antisymmetric contributions to the rectification are presented. The symmetric part changes significantly with microwave frequency omega at omegatau_{f}>/=1, where tau_{f} is the time of the ballistic electron flight across the dot. The results lead consistently towards the ballistic origin of the effect, and can be explained by strongly nonlocal electron response to the microwave electric field, which affects both speed and direction of the electron motion inside the dot.     

Ballistic Aharonov–Bohm quantum bits and quantum gates

We propose an architecture to perform quantum computation, using ballistic electrons as qubits and coupled quantum rings as quantum gates. In the proposed architecture two adjacent one-dimensional wires, creating a single qubit, are connected to two coupled quantum rings, where the required magnetic flux is provided by enclosed nano-sized magnets. The phase modulation of the wave function of the ballistic electrons under the Aharonov–Bohm effect is carefully designed to facilitate reprogrammable and dynamically controllable quantum gates. Arbitrary single-qubit quantum gates with high fidelity can be constructed on the basis of this architecture.     

Magnetization of ballistic quantum dots induced by a linear-polarized microwave field

On a basis of extensive analytical and numerical studies we show that a linear-polarized microwave field creates a stationary magnetization in mesoscopic ballistic quantum dots with two-dimensional electron gas being at a thermal equilibrium. The magnetization is proportional to a number of electrons in a dot and to a microwave power. Microwave fields of moderate strength create in a one dot of few micron size a magnetization which is by few orders of magnitude larger than a magnetization produced by persistent currents. The effect is weakly dependent on temperature and can be observed with existing experimental techniques. The parallels between this effect and ratchets in asymmetric nanostructures are also discussed.     

Vircator with ballistic focusing of an electron beam

A high-power microwave oscillator (vircator) is built around an ironless induction linac. The feature of this device is ballistic focusing of an electron beam in a diode-type system with a concentric spherical cathode and anode. The possibility of the vircator to generate high-power microwave pulses is demonstrated.     

Microwave response of a ballistic quantum dot

The microwave response (photovoltage and photoconductance) of a lateral ballistic quantum dot made of a high-mobility two-dimensional electron gas in an AlGaAs/GaAs heterojunction has been studied experimentally in the frequency range of 110–170 GHz. It has been found that the asymmetry of the photovoltage with respect to the sign of the magnetic field has mesoscopic character and depends on both the magnetic field and the microwave power. This indicates the violation of the Onsager reciprocity relations regarding the electron-electron interactions in the mesoscopic photovoltaic effect. A strong increase in the conductance of the quantum dot induced by the microwave radiation and unrelated to heating, as well as the microwave-induced magneto-oscillations, has been discovered.     

Geometric-symmetry consideration on magneto-conductance oscillations in purely ballistic quantum rings

We report an analysis of the magneto-conductance oscillations in two-dimensional mesoscopic ring structures with different geometric symmetry. In particular, we demonstrate that the h/2e magneto-conductance oscillations may be absent or present in purely ballistic quantum rings depending on their geometric symmetry. A detailed analysis of the results is carried out by expanding the transmission amplitudes with backscattering terms. The role of interchannel scattering, which is an essential element of multichannel ballistic transport, is stressed.     

Normal persistent currents

This article reviews recent advances in mesoscopic physics, namely experimental and theoretical investigations of persistent (equilibrium) currents in normal metal rings. While theory and experiment are consistent in the ballistic regime, theoretical studies so far have not been able to account for the unexpectedly huge currents observed experimentally in disordered (diffusive) samples, in which the elastic mean free path is much less than the circumference of the rings.     

Strong dependence of multichannel ballistic transport on the geometric symmetry

Ballistic electron transport in Aharonov–Bohm-type ring structures is investigated where the single-channel problem is nontrivially extended to the multichannel one in which the important interchannel scattering effect is considered. It is found that theS-matrix of a ring structure should reflect the geometric symmetry if the interchannel scattering effect is properly accounted for and that the symmetry relationships of theS-matrix plays a crucial role in the conductance oscillation behavior in ballistic two-dimensional rings. The magnetostatic as well as the electrostatic Aharonov–Bohm effects are studied for two ring structures of different symmetry.     

Splitting of the resonance levels of double-barrier structures in a high microwave electric field

The dependence of the width and shape of the resonance levels of asymmetric double-barrier resonance-tunneling structures with high narrow barriers on the amplitude of the resonance microwave field and specific features of the electron transport in the case of ballistic passage of electrons near the resonance levels has been investigated. It has been found that a resonance level can be first broadened significantly and be further split into two absolutely transparent levels with an increase in the microwave field amplitude. The conditions have been formulated under which nonresonance scattering channels near the resonance levels also become absolutely transparent.     

基于正六边形多开口的新型双频带左手材料

本文提出了基于正六边形多开口的新型双频带磁谐振体.在微波衬底材料的一面放置交错多开口的两个正六边形金属环,多开口结构破坏了环间耦合电容,从而使两环形成相对独立的两个谐振网络实现双频带效应.最后将该谐振结构的另一面放置金属导线形成一个双频带的新型左手材料.文中利用HFSS软件仿真和等效参数提取的方法,分析和验证该结构的正确性.     

Ballistic anisotropic magnetoresistance

Electronic transport in ferromagnetic ballistic conductors is predicted to exhibit ballistic anisotropic magnetoresistance-a change in the ballistic conductance with the direction of magnetization. This phenomenon originates from the effect of the spin-orbit interaction on the electronic band structure which leads to a change in the number of bands crossing the Fermi energy when the magnetization direction changes. We illustrate the significance of this phenomenon by performing ab initio calculations of the ballistic conductance in ferromagnetic Ni and Fe nanowires which display a sizable ballistic anisotropic magnetoresistance when magnetization changes direction from parallel to perpendicular to the wire axis.     

Spin Hall current driven by quantum interferences in mesoscopic Rashba rings

We propose an all-electrical nanostructure where pure spin current is induced in the transverse voltage probes attached to a quantum-coherent ballistic one-dimensional ring when unpolarized charge current is injected through its longitudinal leads. Tuning of the Rashba spin-orbit coupling in a semiconductor heterostructure hosting the ring generates quasiperiodic oscillations of the predicted spin-Hall current due to spin-sensitive quantum-interference effects caused by the difference in the Aharonov-Casher phase accumulated by opposite spin states. Its amplitude is comparable to that of the spin-Hall current predicted for finite-size (simply connected) two-dimensional electron gases, while it gets reduced gradually in wide two-dimensional rings or due to spin-independent disorder.     

Ballistic transport and spin-orbit interaction of two-dimensional electrons on a cylindrical surface

The components of the ballistic magnetoconductance tensor of a two-dimensional electron gas placed on a cylindrical sector are calculated for various geometries. For a quasiclassical system a method is proposed for finding the conductance based only on the Bohr-Sommerfeld quantization condition and not requiring a knowledge of the matrix elements of the velocity. The effect of curvature of the surface on the spin-orbit interaction in a two-dimensional electron gas is investigated. As examples, the microwave absorption and longitudinal conductance of a hollow cylindrical wire are calculated, and also the conductance of a cylindrical sector. There are qualitative differences from planar systems, in particular the relative sign of the curvature and the spin-orbit coupling constant becomes important. Zh. éksp. Teor. Fiz. 113, 1411–1428 (April 1998)     

Synchronization,zero-resistance states and rotating Wigner crystal

We show, in a framework of a classical nonequilibrium model, that rotational angles of electrons moving in two dimensions (2D) in a perpendicular magnetic field can be synchronized by an external microwave field whose frequency is close to the Larmor frequency. The synchronization eliminates collisions between electrons and thus creates a regime with zero diffusion corresponding to the zero-resistance states observed in experiments with high mobility 2D electron gas (2DEG). For long range Coulomb interactions electrons form a rotating hexagonal Wigner crystal. Possible relevance of this effect of synchronization-induced self-assembly for planetary rings is discussed.     

Weak localization in mesoscopic hole transport: berry phases and classical correlations

We consider phase-coherent transport through ballistic and diffusive two-dimensional hole systems based on the Kohn-Luttinger Hamiltonian. We show that intrinsic heavy-hole-light-hole coupling gives rise to clear-cut signatures of an associated Berry phase in the weak localization which renders the magnetoconductance profile distinctly different from electron transport. Nonuniversal classical correlations determine the strength of these Berry phase effects and the effective symmetry class, leading even to antilocalization-type features for circular quantum dots and Aharonov-Bohm rings in the absence of additional spin-orbit interaction. Our semiclassical predictions are confirmed by numerical calculations.     

Influence of external nonuniform magnetic field on the spectral characteristics of a virtual cathode oscillator’s output radiation

The influence of an external non-uniform magnetic field created using a periodic magnetic focusing system on the spectral characteristics of a virtual cathode oscillator’s output radiation is investigated by means of numerical simulation. It is shown that raising the magnetization intensity of a single magnetic ring or the number of magnetic rings leads to an increase in the output microwave radiation power spectrum’s irregularity. As consequence, the output microwave signal exhibits wide-band oscillations with a bandwidth close to one octave.     

From chaos to disorder: Statistics of the eigenfunctions of microwave cavities

We study the statistics of the experimental eigenfunctions of chaotic and disordered microwave billiards in terms of the moments of their spatial distributions, such as the inverse participation ratio (IPR) and density-density auto-correlation. A path from chaos to disorder is described in terms of increasing IPR. In the chaotic, ballistic limit, the data correspond well with universal results from random matrix theory. Deviations from universal distributions are observed due to disorder induced localization, and for the weakly disordered case the data are well-described by including finite conductance and mean free path contributions in the framework of nonlinear sigma models of supersymmetry.     

Ballistic Quantum Transport: Effect of Geometrical Phases

We study the influence of nonuniform magnetic fields on the magneto conductance of mesoscopic microstructures. We show that the coupling of the electron spin to the inhomogenous field gives rise to effects of the Berry phase on ballistic quantum transport and discuss adiabaticity conditions required to observe such effects. We present numerical results for different ring geometries showing a splitting of Aharonov–Bohm conductance peaks for single rings and corresponding signatures of the geometrical phase in weak localization. The latter features can be qualitatively explained in a semiclassical approach to quantum transport.     

Sagnac effect and Ritz ballistic hypothesis (Review)

It is shown that the Ritz ballistic hypothesis, which is based on the vector summation of the speed of light with the velocity of the radiation source, contradicts the fact of existence of the Sagnac effect. Based on a particular example of a three-mirror ring interferometer, it is shown that the application of the Ritz ballistic hypothesis leads to an obvious calculation error, namely, to the appearance of a difference in the propagation times of counterpropagating waves in the absence of rotation. A review is given of experiments and of results of processing of astronomical observations and discussions devoted to testing the Ritz ballistic hypothesis. A number of other physical phenomena that refute the Ritz ballistic hypothesis are considered.     

Self-generation of spin-wave envelope soliton trains with different periods

The self-generation of periodic spin-wave envelope soliton trains of microwave spin waves in active rings based on ferromagnetic films is studied experimentally. The trains of bright solitons with different periods are self-generated in the same ring due to the frequency-selective control of the attenuation of spin waves circulating in an active ring.