arXiv subjects

V. Ya. Demikhovskii

Publications and source records attributed to V. Ya. Demikhovskii.

At least 19 recordsLinked to original sources

arXiv2015

Nonstandard electron dynamics in topological insulators subjected to magnetic field: the Berry phase effects

The quasiclassical dynamics is studied for charge carriers moving on the surface of 3D topological insulator of Bi2Te3 type and subjected to static magnetic field. The effects connected to the symmetry changes of electron isoenergetic surfaces (contours) and to the nonzero Berry curvature are taken into account. It is shown that in contrast to the standard dynamics of the electrons moving in constant and uniform magnetic field along the trajectories defined by the equations E(k)=const and pz=const, here some new effects are arising, being related to both the appearance of the anomalous velocity term proportional to the Berry curvature, and to the trajectory bending related to the additional term for the energy proportional to the orbital momentum of the wavepacket. This should lead to the changes in cyclotron resonance conditions of the surface electrons. Although the time reversal invariance and the topological order are broken in the magnetic field, the investigation of cyclotron resonance allows determining whether this insulator was trivial or nontrivial at zero magnetic field.

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arXiv2011

The long-term cyclotron dynamics of relativistic wave packets: spontaneous collapse and revival

In this work we study the effects of collapse and revival as well as {\it Zitterbewegung} (ZB) phenomenon, for the relativistic electron wave packets, which are a superposition of the states with quantum numbers sharply peaked around some level $n_0$ of the order of few tens. The probability densities as well as average velocities of the packet center and the average spin components were calculated analytically and visualized. Our computations demonstrate that due to dephasing of the states for times larger than the cyclotron period the initial wave packet (which includes the states with the positive energy only) loses the spatial localization so that the evolution can no longer be described classically. However, at the half-revival time $t=T_R/2$ its reshaping takes place firstly. The behavior of the wave packet containing the states of both energy bands (with $E_n>0$ and $E_n<0$) is more complicated. At short times of a few classical periods such packet splits into two parts which rotate with cyclotron frequency in the opposite directions and meet each other every one-half of the cyclotron period. At these moments their wave functions have significant overlap that leads to ZB. At the time of fractional revival each of two sub-packets is decomposed into few packets-fractions. However, at $t=T_R$ each of the two sub-packets (with positive or negative energy) restores at various points of the cyclotron orbit, that makes it impossible reshaping of initial wave packet entirely unlike the wave packet which consists of states with energies $E_n>0$ only. Obtained results can be useful for the description of electromagnetic radiation and absorption in relativistic plasma on astrophysics objects, where super high magnetic field has the value of the order $10^8-10^9$T, as well as for interpretation of experiments with trapped ions.

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arXiv2010

Space-time evolution of Dirac wave packets

In this work we study the dynamics of free 3D relativistic Gaussian wave packets with different spin polarization. We analyze the connection between the symmetry of initial state and the dynamical characteristics of moving particle. The corresponding solutions of Dirac equation having different types of symmetry were evaluated analytically and numerically and after that the electron probability densities, as well as, the spin densities were visualized. The average values of velocity of the packet center and the average spin were calculated analytically, and the parameters of transient Zitterbewegung in different directions were obtained. These results can be useful for the interpretation of future experiments with trapped ions.

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arXiv2009

Wave packet dynamics in hole Luttinger systems

For hole systems with an effective spin 3/2 we analyzed analytically and numerically the evolution of wave packets with the different initial polarizations. The dynamics of such systems is determined by the $4\times 4$ Luttinger Hamiltonian. We work in the space of arbitrary superposition of light- and heavy-hole states of the "one-particle system". For 2D packets we obtained the analytical solution for the components of wave function and analyzed the space-time dependence of probability densities as well as angular momentum densities. Depending on the value of the parameter $a=k_0d$ ($k_0$ is the average momentum vector and $d$ is the packet width) two scenarios of evolution are realized. For $a>>1$ the initial wave packet splits into two parts and the coordinates of packet center experience the transient oscillations or {\it Zitterbewegung} (ZB) as for other two-band systems. In the case when $a<<1$ the distribution of probability density at $t>0$ remains almost cylindrically symmetric and the ripples arise at the circumference of wave packet. The ZB in this case is absent. We evaluated and visualized for different values of parameter $a$ the space-time dependence of angular momentum densities, which have the multipole structure. It was shown that the average momentum components can precess in the absence of external or effective magnetic fields due to the interference of the light- and heavy hole states. For localized initial states this precession has a transient character.

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arXiv2008

Wave packet dynamics in a monolayer graphene

The dynamics of charge particles described by Gaussian wave packet in monolayer graphene is studied analytically and numerically. We demonstrate that the shape of wave packet at arbitrary time depends on correlation between the initial electron amplitudes $ψ_1(\vec r,0)$ and $ψ_2(\vec r,0)$ on the sublattices $A$ and $B$ correspondingly (i.e. pseudospin polarization). For the transverse pseudospin polarization the motion of the center of wave packet occurs in the direction perpendicular to the average momentum $ {\vec p_0}=\hbar \vec{k_0}$. Moreover, in this case the initial wave packet splits into two parts moving with opposite velocities along $ {\vec p_0}$. If the initial direction of pseudospin coincides with average momentum the splitting is absent and the center of wave packet is displaced at $t>0$ along the same direction. The results of our calculations show that all types of motion experience {\it zitterbewegung}. Besides, depending on initial polarization the velocity of the packet center may have the constant component $v_c=uf(a)$, where $u\approx 10^8 cm/s$ is the Fermi velocity and $f(a)$ is a function of the parameter $a=k_0d$ ($d$ is the initial width of wave packet). As a result, the direction of the packet motion is determined not only by the orientation of the average momentum, but mainly by the phase difference between the up- and low- components of the wave functions. Similar peculiarities of the dynamics of 2D electron wave packet connected with initial spin polarization should take place in the semiconductor quantum well under the influence of the Rashba spin-orbit coupling.

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arXiv2008

Wave packet dynamics in 2DEG with spin orbit coupling: splitting and zitterbewegung

We study the effect of splitting and zitterbewegung of 1D and 2D electron wave packets in the semiconductor quantum well under the influence of the Rashba spin orbit coupling. Results of our investigations show that the spin orbit interaction induces dramatic qualitative changes in the evolution of spin polarized wave packet. The initial wave packet splits into two parts with different spin polarization propagating with unequal group velocity. This splitting appears due to the presence of two branches of electron spectrum corresponding to the stationary states with different chirality. It is demonstrated also that in the presence of external magnetic field B$ perpendicular to the electron gas plane the wave packet splits into two parts which rotates with different cyclotron frequencies. It was shown that after some periods the electron density distributes around cyclotron orbit and the motion acquire an irregular character. Our calculations were made for both cases of weak and strong spin orbit coupling.

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arXiv2007

Hall Conductance of a Two-Dimensional Electron Gas with Spin-Orbit Coupling at the Presence of Lateral Periodic Potential

We evaluate the distribution of Hall conductances in magnetic subbands of two-dimensional electron gas with Rashba spin-orbit (SO) coupling placed in a periodic potential and perpendicular magnetic field. In this semiconductor structure the spin-orbit coupling mixes the states of different magnetic subbands and changes the distribution of their Hall conductances in comparison with the case of spinless particles. The calculations were made for semiconductor structures with a weak ($AlGaAs/GaAs$) and relatively strong ($GaAs/InGaAs$) SO and Zeeman interactions. The Hall conductances of fully occupied magnetic subbands depend on the system parameters and can be changed when neighboring subbands touch each other. It was shown that in the real semiconductor structures with relatively strong SO coupling the distribution of Hall conductance differs from the quantization law predicted by Thouless et al\cite{Thoul} for systems without spin-orbit coupling. In the case of weak SO interaction and relatively large lattice period the Hall conductance of magnetic subbands are the same as for spinless particles, but as the lattice period decreases and two neighboring subbands touch each other the distribution of Hall conductances is changed drastically.

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arXiv2006

Nonlinear electron dynamics in a rippled channel with time-dependent electric field: Quantum Arnol'd diffusion

We study the electron dynamics in a 2D waveguide bounded by a periodically rippled surface in the presence of the time-periodic electric field. The main attention is paid to a possibility of a weak quantum diffusion along the coupling resonance, that can be associated with the classical Arnol'd diffusion. It was found that quantum diffusion is possible only when the perturbation is large enough in order to mix many near-separatrix levels. The rate of the quantum diffusion turns out to be less than the corresponding classical one, thus indicating the influence of quantum coherent effects. Another important effect is the dynamical localization of the quantum diffusion, that may be compared with the famous Anderson localization occurring in 1D random potentials. Our estimates show that the quantum Arnol'd diffusion can be observed in semi-metal rippled channels, for which the scattering and decoherence times are larger than the saturation time due to the dynamical localization.

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arXiv2006

Harper-Hofstadter problem for 2D electron gas with ${\bf k}$-linear Rashba spin-orbit coupling

The Harper-Hofstadter problem for two-dimensional electron gas with Rashba spin-orbit coupling subject to periodic potential and perpendicular magnetic field is studied analytically and numerically. The butterfly-like energy spectrum, spinor wave functions as well as the spin density and average spin polarization are calculated for actual parameters of semiconductor structure. Our calculations show that in two-dimensional electron gas subject to periodic potential and uniform magnetic field the effects of energy spectrum splitting caused by large spin-orbit Rashba coupling can be observed experimentally.

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arXiv2006

Spin-orbit lateral superlattices: energy bands and spin polarization in 2DEG

The Bloch spinors, energy spectrum and spin density in energy bands are studied for the two-dimensional electron gas (2DEG) with Rashba spin-orbit (SO) interaction subject to one-dimensional (1D) periodic electrostatic potential of a lateral superlattice. The space symmetry of the Bloch spinors with spin parity is studied. It is shown that the Bloch spinors at fixed quasimomentum describe the standing spin waves with the wavelength equal to the superlattice period. The spin projections in these states have the components both parallel and transverse to the 2DEG plane. The anticrossing of the energy dispersion curves due to the interplay between the SO and periodic terms is observed, leading to the spin flip. The relation between the spin parity and the interband optical selection rules is discussed, and the effect of magnetization of the SO superlattice in the presence of external electric field is predicted.

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arXiv2005

Quantum Arnol'd diffusion in a rippled waveguide

We study the quantum Arnol'd diffusion for a particle moving in a quasi-1D waveguide bounded by a periodically rippled surface, in the presence of the time-periodic electric field. It was found that in a deep semiclassical region the diffusion-like motion occurs for a particle in the region corresponding to a stochastic layer surrounding the coupling resonance. The rate of the quantum diffusion turns out to be less than the corresponding classical one, thus indicating the influence of quantum coherent effects. Another result is that even in the case when such a diffusion is possible, it terminates in time due to the mechanism similar to that of the dynamical localization. The quantum Arnol'd diffusion represents a new type of quantum dynamics, and may be experimentally observed in measurements of a conductivity of low-dimensional mesoscopic structures.

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arXiv2004

Hall Conductance of a Two-Dimensional Electron Gas in Periodic Lattice with Triangular Antidots

The topic of this contribution is the investigation of quantum states and quantum Hall effect in electron gas subjected to a periodic potential of the lateral lattice. The potential is formed by triangular quantum antidos located on the sites of the square lattice. In a such system the inversion center and the four-fold rotation symmetry are absent. The topological invariants which characterize different magnetic subbands and their Hall conductances are calculated. It is shown that the details of the antidot geometry are crucial for the Hall conductance quantization rule. The critical values of lattice parameters defining the shape of triangular antidots at which the Hall conductance is changed drastically are determined. We demonstrate that the quantum states and Hall conductance quantization law for the triangular antidot lattice differ from the case of the square lattice with cylindrical antidots. As an example, the Hall conductances of magnetic subbands for different antidot geometries are calculated for the case when the number of magnetic flux quanta per unit cell is equal to three.

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arXiv2002

Quantum Hall effect in a p-type heterojunction with a lateral surface quantum dot superlattice

The quantization of Hall conductance in a p-type heterojunction with lateral surface quantum dot superlattice is investigated. The topological properties of the four-component hole wavefunction are studied both in r- and k-spaces. New method of calculation of the Hall conductance in a 2D hole gas described by the Luttinger Hamiltonian and affected by lateral periodic potential is proposed, based on the investigation of four-component wavefunction singularities in k-space. The deviations from the quantization rules for Hofstadter "butterfly" for electrons are found, and the explanation of this effect is proposed. For the case of strong periodic potential the mixing of magnetic subbands is taken into account, and the exchange of the Chern numbers between magnetic subands is discussed.

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arXiv2002

Quantum states and optics in a {\it p}-type heterojunction with lateral surface quantum dot or antidot superlattice subjected to perpendicular magnetic field

The studies of quantum states and optics in a {\it p}-type heterojunction with lateral surface quantum dot (antidot) superlattice and in the presence of perpendicular magnetic field are performed. For the first time the Azbel'-- Hofstadter problem is solved for holes in a complicated valence band described by the $4 \times 4$ Luttinger Hamiltonian. The set of magnetic subbands is obtained for separate hole levels in a wide interval of magnetic field. We found remarkable differences between hole spectra and the Hofstadter "butterfly" for electrons. The influence of the spin-orbit interaction onto wavefunctions and energy spectrum has been investigated. The probabilities of optical transitions between quantum states in the valence band and donors located in the monolayer inside the heterojunction are calculated. The set of parameters (superlattice periods, amplitude of periodic potential, magnitude of magnetic field, etc.) required for experimental observation of splitted hole Landau levels is determined.

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arXiv2002

Quantum Arnol'd Diffusion in a Simple Nonlinear System

We study the fingerprint of the Arnol'd diffusion in a quantum system of two coupled nonlinear oscillators with a two-frequency external force. In the classical description, this peculiar diffusion is due to the onset of a weak chaos in a narrow stochastic layer near the separatrix of the coupling resonance. We have found that global dependence of the quantum diffusion coefficient on model parameters mimics, to some extent, the classical data. However, the quantum diffusion happens to be slower that the classical one. Another result is the dynamical localization that leads to a saturation of the diffusion after some characteristic time. We show that this effect has the same nature as for the studied earlier dynamical localization in the presence of global chaos. The quantum Arnol'd diffusion represents a new type of quantum dynamics and can be observed, for example, in 2D semiconductor structures (quantum billiards) perturbed by time-periodic external fields.

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arXiv2001

Quantum states and magnetooptics in n- and p-type heterojunctions with lateral surface quantum dot (antidot) superlattice subjected to perpendicular magnetic field

The studies of quantum states and optics in n- and p-type heterojunctions with lateral surface quantum dot (antidots) superlattice and in the presence of perpendicular magnetic field are performed. The Azbel' - Hofstadter problem is solved for electrons in conduction band and for holes in valence band described by 4x4 Luttinger Hamiltonian. Under the conditions of non-interactive Landau levels the set of magnetic subbands is obtained for separate electron and hole levels in wide interval of magnetic fields. The influence of spin-orbit interaction onto wavefunctions and energy spectrum in hole magnetic subbands has been investigated. The probabilities of transitions between quantum states in magnetic subbands and monolayer of impurities located inside heterojunction are calculated for two cases: transitions between electron states and acceptors and between hole states and donors. The set of parameters (superlattice periods, amplitude of periodic potential and magntitude of magnetic field, etc.) required for experimental observation of magnetic subbands is found.

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arXiv2001

Manifestation of the Arnol'd Diffusion in Quantum Systems

We study an analog of the classical Arnol'd diffusion in a quantum system of two coupled non-linear oscillators one of which is governed by an external periodic force with two frequencies. In the classical model this very weak diffusion happens in a narrow stochastic layer along the coupling resonance, and leads to an increase of total energy of the system. We show that the quantum dynamics of wave packets mimics, up to some extent, global properties of the classical Arnol'd diffusion. This specific diffusion represents a new type of quantum dynamics, and may be observed, for example, in 2D semiconductor structures (quantum billiards) perturbed by time-periodic external fields.

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arXiv1999

Formation of New Fermi Surfaces in 3D Crystals at Ultra High Magnetic Field with Different Orientations

In the tight-binding approximation the Harper like equation describing an electron in 3D crystal subject to a uniform magnetic field is obtained. It is supposed that the vector H can be oriented along several directions in the lattice. The Fermi surfaces relevant to a magnetic flux p/q=1/2 in a simple cubic lattice are built. The quantization rules in magnetic fields slightly distinguished from p/q=1/2 are investigated.

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