Cyclotron dynamics of electron wave packets in topological insulators in an external magnetic field

The evolution of electron wave packets formed from surface states in topological insulators located in an external magnetic field is studied. The electron and spin densities of the wave packets under consideration are calculated analytically and are visualized. The influence of the main characteristics of the wave packets (the spin polarization) on the splitting and the change in their forms with time is considered.     

Wave packet splitting and zitterbewegung in two-dimensional semiconductor structures with spin-orbit coupling

Dynamics of electron wave packets in an asymmetric quantum well in the presence of Rashba spinorbit coupling was analytically and numerically studied. Electron Green’s functions were introduced and the evolution of 1D and 2D wave packets was studied. The effect of packet splitting caused by the presence of two branches with different chiralities in the Rashba Hamiltonian spectrum and zitterbewegung, i.e., packet center’s jitter, was studied. Spatial components of the spin density were calculated. It was shown that the component of the spin density S _y in split parts of the wave packet has opposite signs, and two other spin density components oscillate in space between scattering packets.     

Spin dependent 2D electron scattering by nanomagnets

The 2D scattering problem of an electron by a magnetized nanoparticle is solved in the Born approximation with account of the dipole-dipole interaction of the magnetic moments of electron and nanomagnet. The scattering amplitudes in this problem are the two-component spinors. They are obtained as functions of the electron spin orientation, the electron energy and show anisotropy in scattering angle. The initially polarized beam of electrons scattered by the nanomagnet consists of electrons with no spin flipped and spin flipped. The majority of electrons with no spin flipped are scattered by small angles. The majority electrons with spin flipped are scattered in the vicinity of the scattering angles π/2 and 3π/2. This can be used as one more method of controlling the spin currents.     

Dynamics of electron wave packets in topological insulators

Dynamics of wave packets formed by surface (edge) electronic states in topological insulators has been investigated. The spin and electron probability density, as well as zitterbewegung, of wave packets have been calculated analytically and numerically for various values of the Hamiltonian parameters. The effects of the main parameters (size and spin polarization) of the wave packets on a change in the packet shape and oscillations of their average velocity have been considered.     

Scattering of Wave Packets on the Surface of Topological Insulators in the Presence of Potential Barriers with Magnetization

The nonstationary Schrödinger equation is solved numerically by the Cayley method for wave packets that are formed from surface states on the surface of topological insulators and are scattered by a potential barrier, including a barrier with magnetization. The transmission coefficient and spin density distributions are calculated. Expressions are found for the static transmission coefficient through a barrier with the use of the plane-wave approximation and its generalization for wave packets. It is shown that the two-dimensional nature of wave packets leads to noticeable differences in the behavior of the transmission coefficient compared to that in the plane-wave scattering problem. For instance, two-dimensional packets exhibit a significant suppression of Klein tunneling in some energy regions. The results obtained show that the tunneling and spin density of localized wave-packet-type electronic states in structures based on topological insulators can be affected through potential barriers.     

Magnetic and orbital dichroism in (e,2e) ionization of sodium

We present the first measurement of (e,2e) ionization cross sections for a laser oriented atomic target by spin polarized electrons. Cross sections are presented as a function of target orientation and polarization direction of the incident electron beam. This study provides insight into mechanisms by which angular momentum is transferred from the valence electron to the two final-state continuum electrons in both singlet and triplet spin channels, by comparing measurement with distorted wave Born approximation and the dynamically screened three Coulomb wave calculations.     

Correlation quantum dynamics between an electron and D+2 molecule with attosecond resolution

Recently, Niikura et al. [Nature (London) 421, 826 (2003)] have applied the entanglement approach to exploit the correlation between the electronic and nuclear wave packets. Here, we use the time-dependent-wave-packet method to calculate the kinetic energy distribution of the D+ ion resulting from the recollision between an electron and its parent ion D+2(X2Sigma+g) within the attoseconds time scale. Our theoretical results of the D+ ion kinetic energy spectra accord well with the experimental ones, and the recollision probabilities between the electron and the D+2 molecule have been calculated.     

Specific features of the electron paramagnetic resonance spectrum in the vicinity of the convergence of the transitions of gadolinium centers in Pb5(Ge1 − x Si x )3O11

An anomalous electron paramagnetic resonance spectrum of the transitions ?1/2 ? +1/2 of four Gd³⁺-Si dimer clusters in the Pb₅(Ge_{1 ? x} Si _x )₃O₁₁ crystals doped with gadolinium has been found in the vicinity of the orientation of the magnetic field along the optic axis of the crystal. It has been assumed that this spectrum is caused by rapid transitions between the spin packets of the initial resonances due to the crossrelaxation. A computer simulation of the spectrum has been carried out. The results obtained adequately describe the experiment.     

A method for constructing radial wave packets with application to target distortion in electron-atom collisions

It has been shown that an analysis of radial stationary state wave functions of a particle in terms of their loops leads to such continuous, single-valued and finite functions which represent a practically convenient form of the radial wave packets of that particle at various positions. The radial wave packets have been used to investigate target distortion in electron-atom collisions. The distortion of the target is defined in terms of quantum-mechanical probabilities given by the wave packets. A closed expression which depends upon the position of the colliding electron, is obtained for the potential energy of the target in the field of the colliding electron.     

Magnetism and superconductivity in a quasi-2D anisotropic system doped with charge carriers

The theory of multiband superconducting systems with variable density of charge carriers is analyzed. The possibility of emergence of nonphonon high-temperature superconductivity due to the predominance of electron–electron interband interactions over intraband interactions, as well as due to the fact that the thermodynamic and magnetic properties of multiband systems in the superconducting phase differ qualitatively from those of single-band systems, is indicated. Phase transitions in a quasi-2D anisotropic medium upon a change in the carrier concentration, i.e., a transition from the commensurate to the incommensurate state of the spin density wave, are analyzed. Such a transition is observed when the Umklapp processes in the lattice structure are taken into account. These processes facilitate a deviation of wavevector Q of the spin density wave from 2k_F, as well as a displacement of the bandgap relative to the Fermi surface. This leads to the generation of free charge carriers and the possibility of superconductivity. It is shown that superconductivity accompanies the magnetism. The conditions for the coexistence of these two phenomena are determined.     

Optical orientation by linearly polarized light in intersubband quantum-well transitions

The absorption of linearly polarized light in low-dimensional semiconductor structures is investigated. It is shown that the absorption under consideration can give rise to spin orientation of free carriers. A theory of this optical orientation by linearly polarized light is developed for resonant intersubband optical transitions in n-type quantum wells. It is demonstrated that, in the vicinity of the resonance, the optical orientation undergoes spectral inversion, namely, the electron spin orientation reverses sign with increasing frequency. This behavior can be accounted for by the spin-orbit subband splitting, which is linear in the wave vector, and by the energy and quasi-momentum conservation laws.     

Fidelity of Two-Particle Wave Packets Moving around the Schwarzschild Spacetime

Fidelity for two-particle wave packets of spin- particles moving around the Schwarzschild spacetime is discussed. Both acceleration and gravity cause to produce a Wigner rotation that transforms the wave packet as it moves along a specified path in the gravitational field. For considered circular paths, the fidelity between the spin parts of initial and final states of the system, called the spin fidelity, is obtained as a function of angular velocity, elapsed proper time and radius of circular paths. For fixed elapsed proper time and angular momentum of the centroid, there always exists one circular orbit with determined radius on which the fidelity of spin parts is minimum. Using a numerical approach, the behavior of the spin fidelity in terms of the angular velocity, as well as the radius of paths is described for both the spin singlet and spin triplet states.     

Quantum computing through electron propagation in edge states of quantum spin Hall systems

We propose to implement quantum computing by the on-demand control of the wave packets propagation in helical edge channels of the quantum spin Hall systems (QSHs). Two non-commutative single-qubit gates are realized by the gate voltages applied on the edge channels. The two-qubit controlled phase gate is implemented by the capacitive Coulomb interaction between two adjacent edge channels from two parallel QSHs. A universal set of quantum gates thus can be realized in an all-electrical way. It is also shown that the fidelity and the purity of the controlled phase gate can reach a high value, with both the time delay and the finite width of the wave packets taken into account.     

Wave packet echoes in the motion of trapped atoms

We experimentally demonstrate and systematically study the stimulated revival (echo) of motional wave packet oscillations. For this purpose, we prepare wave packets in an optical lattice by nonadiabatically shifting the potential and stimulate their reoccurrence by a second shift after a variable time delay. This technique, analogous to spin echoes, enables one even in the presence of strong dephasing to determine the coherence time of the wave packets. We find that for strongly bound atoms it is comparable to the cooling time and much longer than the inverse of the photon scattering rate.     

Photoproduction of neutrino pairs on an electron in a magnetic field

The spectral-angular and spectral distributions of the probability of photoproduction of neutrino pairs on an electron in a magnetic field are calculated. The dependence of the probability of this process on the magnetic-field strength, the orientation of the electron spin in the initial and final states, and also on the direction of the circular polarization of the wave is investigated.     

Self-generation of two-dimensional spin-wave bullets

The experimental observation of self-generation of two-dimensional, self-focusing nonlinear spin wave packets-spin wave bullets-in an active ring is reported. The ring is composed of a ferrite film with two antennae for excitation and detection of the wave packets, and a microwave amplifier connecting the antennae and closing the ring. Experimental observation has been made by using the time and space resolved Brillouin light scattering technique. The parameters of spin wave bullets self-generated from noise in an active ring are similar to those of bullets coherently excited by external microwave pulses. The observed self-generation process provides unambiguous evidence that wave bullets are intrinsic excitations of a two-dimensional nonlinear medium with dissipation that is focusing in both directions.     

Microwave electric field induced spin transitions of AlAs 2D electrons

We present the first direct electron spin resonance (ESR) on a 2D electron gas in a III–V semiconductor. ESR on a high mobility 2D electron gas in a single AlAs quantum well reveals an electronic g-factor of 1.991 at 9.35 GHz and 1.989 at 34 GHz with a minimal linewidth of 7 Gauss. Both the signal amplitude and its dependence on the position and orientation of the sample in the cavity unambiguously demonstrate that the spin transitions in our experiment are caused by the microwave electric field. We present a model that ascribes the spin transitions to the effective magnetic field acting on the electron spins that arises from (Bychkov–Rashba) spin-orbit interaction and the modulation of the electron wavevector around k_F induced by the microwave electric field.     

Zitterbewegung of wave packets and conductance of a quasi-one-dimensional channel in the presence of spin-orbit coupling

The electron energy spectrum and wave functions for a quasi-one-dimensional channel with Rashba spin-orbit coupling are calculated. The dynamics of wave packets in thin wires based on GaAs/In_0.23Ga_0.77As and AlGaAs/GaAs heterostructures with Rashba spin-orbit coupling are studied. Spin polarizations are found. The effect of splitting of wave packets with respect to their centers of mass and Zitterbewegung of their centers are discovered. The characteristics of wave-packet oscillations and spin density for free electrons and under confinement conditions are compared. A method for controlling the conductance of the quasi-one-dimensional channel using a controlling electrode is proposed.     

Scattering induced spin orientation and spin currents in gyrotropic structures

It is shown that additional contributions both to current-induced spin orientation and to the spin Hall effect arise in quantum wells due to the gyrotropy of the structures. Microscopically, they are related to the basic properties of gyrotropic systems, namely, to linearity in the wave vector terms in the matrix element of electron scattering and in the energy spectrum. Calculation shows that, in high-mobility structures, the contribution to the spin Hall current considered here can exceed the term originating from the Mott skew scattering. The text was submitted by the author in English.