arXiv subjects

J. Berakdar

Publications and source records attributed to J. Berakdar.

At least 19 recordsLinked to original sources

arXiv2023

Steering skyrmions with microwave and THz electric pulses

Tools for controlling electrically the motion of magnetic skyrmions are important elements towards their use in spintronic devices. Here, we propose and demonstrate the transport of skyrmions via GHz and THz electric pulses. The method relies on using polarization textured pulses such that the skyrmion experiences (via its inherent magnetoelectricity) the out-of-plane and in-plane components of the pulse electric field. It is shown how the electric field drags efficiently the skyrmion. The control of the skyrmion motion depends solely on the amplitude of electric fields, frequency, polarization, or phase in case two pulses are applied. Micromagnetic calculations supported by analytic modeling and analysis indicate the experimental feasibility of the control scheme.

cond-mat.str-el↗

arXiv2022

Rectification of the spin Seebeck current in noncollinear antiferromagnets

In the absence of an external magnetic field and a spin-polarized charge current, an antiferromagnetic system supports two degenerate magnon modes. An applied thermal bias activates the magnetic dynamics, leading to a magnon flow from the hot to the cold edge (magnonic spin Seebeck current). Both degenerate bands contribute to the magnon current but the orientations of the magnetic moments underlying the magnons are opposite in different bands. Therefore, while the magnon current is nonzero, the net spin current is zero.

cond-mat.mes-hall↗

arXiv2021

Directional scrambling of quantum information in helical multiferroics

Local excitations as carriers of quantum information spread out in the system in ways governed by the underlying interaction and symmetry. Understanding this phenomenon, also called quantum scrambling, is a prerequisite for employing interacting systems for quantum information processing. The character and direction dependence of quantum scrambling can be inferred from the out-of-time-ordered commutators (OTOCs) containing information on correlation buildup and entanglement spreading. Employing OTOC, we study and quantify the directionality of quantum information propagation in oxide-based helical spin systems hosting a spin-driven ferroelectric order. In these systems, magnetoelectricity permits the spin dynamics and associated information content to be controlled by an electric field coupled to the emergent ferroelectric order. We show that topologically nontrivial quantum phases, such as chiral or helical spin ordering, allows for electric-field controlled anisotropic scrambling and a direction-dependent buildup of quantum correlations. Based on general symmetry considerations, we find that starting from a pure state (e.g., the ground state) or a finite temperature state is essential for observing directional asymmetry in scrambling. In the systematic numerical studies of OTOC, we quantify the directional asymmetry of the scrambling and verify the conjectured form of the OTOC around the ballistic wavefront. The obtained direction-dependent butterfly velocity $v_{\mathrm{B}}(\mathbf{n})$ provides information on the speed of the ballistic wavefront. In general, our calculations show an early-time power-law behavior of OTOC, as expected from an analytic expansion for small times. The long-time behavior of OTOC reveals the importance of (non-)integrability of the underlying Hamiltonian as well as the implications of conserved quantities such as the $z$-projection of the total spin.

cond-mat.str-el↗

arXiv2020

Generation of coherence in an exactly solvable nonlinear nanomechanical system

This study is focused on the quantum dynamics of a nitrogen-vacancy (NV) center coupled to a nonlinear, periodically driven mechanical oscillator. For a continuous periodic driving that depends on the position of the oscillator, the mechanical motion is described by Mathieu elliptic functions. This solution is employed to study the dynamics of the quantum spin system including environmental effects and to evaluate the purity and the von Neumann entropy of the NV-spin. The unitary generation of coherence is addressed. We observe that the production of coherence through a unitary transformation depends on whether the system is prepared initially in mixed state. Production of coherence is efficient when the system initially is prepared in the region of the separatrix (i.e., the region where classical systems exhibit dynamical chaos). From the theory of dynamical chaos, we know that phase trajectories of the system passing through the homoclinic tangle have limited memory, and therefore the information about the initial conditions is lost. We proved that quantum chaos and diminishing of information about the mixed initial state favors the generation of quantum coherence through the unitary evolution. We introduced quantum distance from the homoclinic tangle and proved that for the initial states permitting efficient generation of coherence, this distance is minimal.

quant-ph↗

arXiv2020

Electron-magnon spin conversion and magnonic spin pumping in antiferromagnet/heavy metal heterostructure

We study the exchange between electron and magnon spins at the interface of an antiferromagnet and a heavy metal at finite temperatures. The underlying physical mechanism is based on spin torque associated with the creation/annihilation of thermal magnons with right-hand and left-hand polarization. The creation/annihilation process depends strongly on the relative orientation between the polarization of the electron and the magnon spins. For a sufficiently strong spin transfer torque (STT), the conversion process becomes nonlinear, generating a nonzero net spin pumping current in the AFM that can detected in the neighboring metal layer. Applying an external magnetic field renders possible the manipulation of the STT driving thermal spin pumping. Our theoretical results are experimentally feasible and are of a direct relevance to antiferromagnet-based spintronic devices.

cond-mat.mes-hall↗

arXiv2020

Stratonovich-Ito integration scheme in ultrafast spin caloritronics

The magnonic spin Seebeck effect is a key element of spin caloritronic, a field that exploits thermal effects for spintronic applications. Early studies were focused on investigating the steady-state nonequilibrium magnonic spin Seebeck current, and the underlying physics of the magnonic spin Seebeck effect is now relatively well established. However, the initial steps of the formation of the spin Seebeck current are in the scope of recent interest. To address this dynamical aspect theoretically we propose here a new approach to the time-resolved spin Seebeck effect. Our method exploits the supersymmetric theory of stochastics and Ito - Stratonovich integration scheme. We found that in the early step the spin Seebeck current has both nonzero transversal and longitudinal components. As the magnetization dynamics approaches the steady-state, the transversal components decay through dephasing over the dipole-dipole reservoir. The time scale for this process is typically in the sub-nanoseconds pointing thus to the potential of an ultrafast control of the dynamical spin Seebeck during its buildup.

cond-mat.mes-hall↗

arXiv2020

The optical tweezer of ferroelectric skyrmions

Strong magneto-electric coupling in two-dimensional helical materials leads to a peculiar type of topologically protected solutions -- skyrmions. Coupling between the net ferroelectric polarization and magnetization allows control of the magnetic texture with an external electric field. In this work we propose the model of optical tweezer -- a particular configuration of an external electric field and Gaussian laser beam that can trap or release the skyrmions in a highly controlled manner. Functionality of such a tweezer is visualized by micromagnetic simulations and model analysis.

cond-mat.mtrl-sci↗

arXiv2019

Spin-orbit-coupled quantum memory of a double quantum dot

The concept of quantum memory plays an incisive role in the quantum information theory. As confirmed by several recent rigorous mathematical studies, the quantum memory inmate in the bipartite system $ρ_{AB}$ can reduce uncertainty about the part $B$, after measurements done on the part $A$. In the present work, we extend this concept to the systems with a spin-orbit coupling and introduce a notion of spin-orbit quantum memory. We self-consistently explore Uhlmann fidelity, pre and post measurement entanglement entropy and post measurement conditional quantum entropy of the system with spin-orbit coupling and show that measurement performed on the spin subsystem decreases the uncertainty of the orbital part. The uncovered effect enhances with the strength of the spin-orbit coupling. We explored the concept of macroscopic realism introduced by Leggett and Garg and observed that POVM measurements done on the system under the particular protocol are non-noninvasive. For the extended system, we performed the quantum Monte Carlo calculations and explored reshuffling of the electron densities due to the external electric field.

quant-ph↗

arXiv2019

High-fidelity magnonic gates for surface spin waves

We study the propagation of surface spin waves in two wave guides coupled through the dipole-dipole interaction. Essential for the observations made here is the magneto-electric coupling between the spin waves and the effective ferroelectric polarization. This allows an external electric field to act on spin waves and to modify the band gaps of magnonic excitations in individual layers. By an on/off switching of the electric field and/or varying its strength or direction with respect to the equilibrium magnetization, it is possible to permit or ban the propagation of the spin waves in selected waveguide. We propose experimentally feasible nanoscale device operating as a high fidelity surface wave magnonic gate.

cond-mat.str-el↗

arXiv2019

Conduction of surface electrons in a topological insulator with spatially random magnetization

Using the Green functions method we study transport properties of surface electrons in topological insulators in the presence of a correlated random exchange field. Such an exchange field may be due to random magnetization with correlated fluctuations. We determine the relaxation time due to scattering from the magnetization fluctuations and from other structural defects. Then we calculate the longitudinal charge conductivity taking into account the contribution due to vertex correction.

cond-mat.mes-hall↗

arXiv2019

From chaos to many-body localization: some introductory notes

Staring from the kicked rotator as a paradigm for a system exhibiting classical chaos, we discuss the role of quantum coherence resulting in dynamical localization in the kicked quantum rotator. In this context, the disorder-induced Anderson localization is also discussed. Localization in interacting, quantum many-body systems (many-body localization) may also occur in the absence of disorder, and a practical way to identify its occurrence is demonstrated for an interacting spin chain.

cond-mat.stat-mech↗

arXiv2019

Thermally assisted Skyrmion drag in a nonuniform electric field

Magnetic skyrmions are topologically protected excitations of the magnetization vector field with promising applications in spintronics and spin-caloritronics, particularly due to their high mobility. Skyrmions can be steered by a spin-polarized charge current or by exposure to a magnonic spin current. Here, we propose a further method for driving skyrmions by applying an inhomogeneous electric field and a homogeneous thermal bias. We show that the inhomogeneous electric torque leads to an efficient skyrmionic drag which can be thermally assisted as to enhance the skyrmion velocity. The calculations and analysis are limited to insulating samples; for conducting materials the influence of the inhomogeneous electric field on the charge carriers need to be taken also into account.

cond-mat.mes-hall↗

arXiv2018

Influence of spin-orbit and spin-Hall effects on the spin Seebeck current beyond linear response

We study the spin transport theoretically in heterostructures consisting of a ferromagnetic metallic thin film sandwiched between heavy-metal and oxide layers. The spin current in the heavy metal layer is generated via the spin Hall effect, while the oxide layer induces at the interface with the ferromagnetic layer a spin-orbital coupling of the Rashba type. Impact of the spin Hall effect and Rashba spin-orbit coupling on the spin Seebeck current is explored with a particular emphasis on nonlinear effects. Technically, we employ the Fokker-Planck approach and contrast the analytical expressions with full numerical micromagnetic simulations. We show that when an external magnetic field is aligned parallel (antiparallel) to the Rashba field, the spin-orbit coupling enhances (reduces) the spin pumping current. In turn, the spin Hall effect and the Dzyaloshinskii-Moriya interaction are shown to increase the spin pumping current.

cond-mat.mes-hall↗

arXiv2018

Thermoelastic enhancement of the magnonic spin Seebeck effect in thin films and bulk samples

A non-uniform temperature profile may generate a pure spin current in magnetic films, as observed for instance in the spin Seebeck effect. In addition, thermally induced elastic deformations may set in that could affect the spin current. A self-consistent theory of the magnonic spin Seebeck effect including thermally activated magneto-elastic effects is presented and analytical expressions for the thermally activated deformation tensor and dispersion relations for coupled magneto-elastic modes are obtained. We derived analytical results for bulk (3D) systems and thin magnetic (2D) films. We observed that the displacement vector and the deformation tensor in bulk systems decay asymptotically as $u\sim1/R^{2}$ and $\varepsilon\sim1/R^{3}$, respectively, while the decays in thin magnetic films proceed slower following $u\sim1/R$ and $\varepsilon\sim1/R^{2}$. The dispersion relations evidence a strong anisotropy in the magnetic excitations. We observed that a thermoelastic steady state deformation may lead to both an enchantment or a reduction of the gap in the magnonic spectrum. The reduction of the gap increases the number of magnons contributing to the spin Seebeck effect and offers new possibilities for the thermoelastic control of the Spin Seebeck effect.

cond-mat.mes-hall↗

arXiv2018

Magnetophononics: ultrafast spin control through the lattice

Using a combination of first-principles and magnetization-dynamics calculations, we study the effect of the intense optical excitation of phonons on the magnetic behavior in insulating magnetic materials. Taking the prototypical magnetoelectric \CrO\ as our model system, we show that excitation of a polar mode at 17 THz causes a pronounced modification of the magnetic exchange interactions through a change in the average Cr-Cr distance. In particular, the quasi-static deformation induced by nonlinear phononic coupling yields a structure with a modified magnetic state, which persists for the duration of the phonon excitation. In addition, our time-dependent magnetization dynamics computations show that systematic modulation of the magnetic exchange interaction by the phonon excitation modifies the magnetization dynamics. This temporal modulation of the magnetic exchange interaction strengths using phonons provides a new route to creating non-equilibrium magnetic states and suggests new avenues for fast manipulation of spin arrangements and dynamics.

cond-mat.str-el↗

arXiv2018

Electric control of emergent magnonic spin current and dynamic multiferroicity in magnetic insulators at finite temperatures

Conversion of thermal energy into magnonic spin currents and/or effective electric polarization promises new device functionalities. A versatile approach is presented here for generating and controlling open circuit magnonic spin currents and an effective multiferroicity at a uniform temperature with the aid of spatially inhomogeneous, external, static electric fields. This field applied to a ferromagnetic insulator with a Dzyaloshinskii-Moriya type coupling changes locally the magnon dispersion and modifies the density of thermally excited magnons in a region of the scale of the field inhomogeneity. The resulting gradient in the magnon density can be viewed as a gradient in the effective magnon temperature. This effective thermal gradient together with local magnon dispersion result in an open-circuit, electric field controlled magnonic spin current. In fact, for a moderate variation in the external electric field the predicted magnonic spin current is on the scale of the spin (Seebeck) current generated by a comparable external temperature gradient. Analytical methods supported by full-fledge numerics confirm that both, a finite temperature and an inhomogeneous electric field are necessary for this emergent non-equilibrium phenomena. The proposal can be integrated in magnonic and multiferroic circuits, for instance to convert heat into electrically controlled pure spin current using for example nanopatterning, without the need to generate large thermal gradients on the nanoscale.

cond-mat.mes-hall↗

arXiv2017

Current-induced spin polarization in isotropic k-cubed Rashba model: Theoretical study for p-doped semiconductor heterostructures and perovskite oxides interfaces

Using the Matsubara Green's function formalism we calculate the temperature dependence of the nonequilibrium spin polarization induced by an external electric field in the presence of spin-orbit coupling. The model Hamiltonian includes an isotropic k-cubed form of the Rashba spin-orbit interaction. Such a Hamiltonian captures the electronic and spin properties of two-dimensional electron (hole) gas at the surfaces or interfaces of transition metal oxides or in p-doped semiconductor heterostructures. The induced spin polarization is calculated for the nonmagnetic as well as magnetic electron/hole gas. Relation of the spin polarization to the Berry curvature is also discussed.

cond-mat.mes-hall↗

arXiv2017

Thermally-induced spin polarization in a magnetized two-dimensional electron gas with Rashba spin-orbit interaction

Spin polarization induced by a temperature gradient (heat-current) in a magnetized two-dimensional electron gas (2DEG) with Rashba spin-orbit interaction is considered theoretically within the linear response theory. Using the Matsubara Green function formalism we calculate the temperature dependence of the spin polarization for arbitrary orientation of the exchange field. The limit of a nonmagnetic 2DEG (zero exchange field) is also considered. The physical mechanisms of the spin polarization within our scheme are discussed.

cond-mat.mes-hall↗