arXiv subjects

Jamal Berakdar

Publications and source records attributed to Jamal Berakdar.

At least 37 records · Page 2Linked to original sources

arXiv2023

PT-symmetry enabled spintronic thermal diode and logic gates

Devices for performing computation and logic operations with low-energy consumption are of key importance for environmentally friendly data-processing and information technology. Here, we present a design for magnetic elements that use excess heat to perform logic operations. The basic information channel is coupled non-conductive magnetic stripes with a normal metal spacer. The thermal information signal is embodied in magnetic excitations and it can be transported, locally enhanced, and controllably steered by virtue of charge current pulses in the spacer. Functionality of essential thermal logic gates is demonstrated by material-specific simulations. The operation principle takes advantage of the special material architecture with a balanced gain/loss mechanism for magnetic excitation which renders the circuit parity-time symmetric with exceptional points tunable by the current strength in the spacer. Heat flow at these points can be enhanced, be non-reciprocal, or may oscillate between the information channels enabling so controlled thermal diode and thermal gate operations. The findings point to a new route for exploiting heat for useful work on the nanoscale.

cond-mat.mes-hall↗

arXiv2022

Mean-field ground-state phase diagram of the ${t-t^\prime}$ ionic-Hubbard chain

Ground state (GS) phase diagram of the one dimensional repulsive Hubbard model with both nearest neighbor ($t$) and next-nearest-neighbor ($t^{\prime}$) hopping and a staggered potential ($Δ$) is determined in the case of half-filled band and zero net magnetization within the mean-field theory. The model may be realized by cold atoms in engineered optical lattices. Connection between the peculiarities of the GS phase diagram of the interacting system and the topological Lifshitz transition in GS of free particle chain is discussed. The mean-field Hamiltonian is given by six order parameters, which are determined self-consistently. It is shown that the GS phase diagram {\em predominantly} consists of insulating phases characterized by coexistence of the long-range ordered modulations of the charge- (I) and antiferromagnetic (AF) spin-density with wavelengths equal to two and/or four lattice units. Below the Lifshitz transition, the GS phase diagram is qualitatively similar to that of the standard (${t^{\prime}=0}$) ionic Hubbard model. After the Lifshitz transition, charge- and spin-density modulations emerge within the sublattices and have wavelengths equal to four lattice units. For moderate values of the on-site repulsion the insulating phases are characterized by the presence of I and AF modulations coexisting with ferrimagnetic spin- and charge-density modulations within the one sublattice, or by the coexistence of I order and additional AF spin density modulation only within the sublattice with high ionic potential. At large repulsion the insulating phase with AF order inside both sublattices and remaining small ionicity left between the sublattices is realized.

cond-mat.str-el↗

arXiv2022

Magnon dynamics in parity-time-symmetric dipolarly coupled waveguides and magnonic crystals

We consider the magnonic properties of two dipolarly coupled magnetic stripes, both deposited on a normal conductive substrate with strong spin-orbit coupling. A charge current in the substrate acts on the adjacent magnets with spin-orbit torques, which result in magnonic damping or antidamping of the spin waves, and hence a gain-loss coupling of the two magnetic stripes. The whole setup is demonstrated to exhibit features typical for parity-time (PT) symmetric systems. Phenomena are demonstrated that can be functionalized in magnonic devices, including reconfigurable magnonic diodes and logic devices. Alternative stripes designs and PT-symmetric, periodic, coupled magnonic textures are studied. Analytical and full numerical analysis identify the conditions for the appearance of exceptional points (EPs), where magnonic gain and loss are balanced and evidence nonreciprocal magnon propagation and enhanced magnon excitation around EPs. Furthermore, the dipolar coupling is shown to bring in a wave vector-dependent PT-symmetric behavior. Proposing and simulating a PT-symmetric magnonic crystal, we show how EPs and hence associated phenomena can be steered to a particular wave vector in a gaped spectrum via material design. The phenomena offer additional tools for magnonic-based communication and computational devices.

cond-mat.str-el↗

arXiv2022

Standing spin wave excitation in Bi:YIG films via temperature induced anisotropy changes and magnetoacoustic coupling

Based on micromagnetic simulations and experimental observations of the magnetization and lattice dynamics following the direct optical excitation of the magnetic insulator Bi:YIG or indirect excitation via an optically opaque Pt/Cu double layer, we disentangle the dynamical effects of magnetic anisotropy and magnetoelastic coupling. The strain and temperature of the lattice are quantified via modeling ultrafast x-ray diffraction data. Measurements of the time-resolved magneto-optical Kerr effect agree well with the magnetization dynamics simulated according to the excitation via two mechanisms: The magneto-acoustic coupling to the experimentally verified strain dynamics and the ultrafast temperature-induced transient change in the magnetic anisotropy. The numerical modeling proves that for direct excitation both mechanisms drive the fundamental mode with opposite phase. The relative ratio of standing spin-wave amplitudes of higher order modes indicates that both mechanisms are substantially active.

cond-mat.other↗

arXiv2021

Spatio-temporal delay in photoionization by polarization structured laser fields

Focused laser fields with textured polarization on a sub-wavelength scale allow extracting information on electronic processes which are not directly accessible by homogeneous fields. Here, we consider photoionization in radially and azimuthally polarized laser fields and show that, due to the local polarizations of the transversal and the longitudinal laser electric field components, the detected photoelectron spectra depend on the atom position from which the electron originates. The calculation results reported here show the angular dependence of the photoionization amplitude, the quantum phase, and the time delay of the valence shell electrons as the parent atom's position varies across the laser spot. We discuss the possibility of using the photoelectron spectra to identify the position of the ionized atom within the laser spot on the sub-wavelength scale. The proposal and its illustrations underline the potential for the detection of the atomic position based on attosecond streaking methods.

physics.atom-ph↗

arXiv2021

Photoelectron emission via time and phase-tailored electromagnetic fields

The energy and the angular distributions of photoelectrons are shown to be tunable by choosing the time and the spatial phase structure of the driving fields. These conclusions are derived from quantum mechanical calculations done within a single-active electron model for an atomic target subjected to a combination of laser field and a time-asymmetric THz pulse and/or vortex-laser pulse with a spatially modulated phase of the wavefront.

physics.atom-ph↗

arXiv2020

Electrons in intense laser fields with local phase, polarization, and skyrmionic textures

Laser fields can be shaped on a subwavelength scale as to have a specific distribution in spin angular momentum, orbital structure, or topology. We study how these various features affect the strongly nonlinear electron dynamics. Specifically, we derive closed expressions for the wave function of an unbound electron subject to a generally structured, intense laser field and demonstrate its use for imprinting the orbital angular momentum of a propagating optical vortex onto photoelectrons emitted from atoms and traveling through the optical vortex. It is also shown that photoelectrons can be accelerated or momentum textured when moving through a focused, intense laser field whose spin angular momentum is modulated as to have a radial polarization, which also implies the presence of a strong electrical longitudinal component. Further results are presented on the subwavelength spatiotemporal imaging of a laser field topology, as demonstrated explicitly for the field's spin and orbital distributions of lossless propagating optical skyrmions imaged by photoelectrons.

quant-ph↗

arXiv2020

Quantum teleportation by utilizing helical spin chains for sharing entanglement

We develop a new protocol for sharing entanglement (one ebit) between two parties using the natural dynamics of helical multiferroic spin chains. We introduce a novel kicking scheme of the electric field for enhancing the teleportation fidelity in our protocol that works in the presence of an appropriate choice of parameters. We also investigate the effect of a common spin environment causing decoherence in the entanglement sharing channel. We compare the results to that of XXZ and XX models subject to a similar entanglement sharing protocol and find that the helical multiferroic chain with the kicking scheme provides a better singlet fraction. We show that the kicking scheme in conjugation with the optimized parameters enhances the fidelity of teleportation even in the presence of impurities and/or decoherence. The advantage of the kicking scheme shown in the impurity cases is an important result to be useful in a realizable setup of helical multiferroic spin chain.

quant-ph↗

arXiv2020

Highly Tunable Spin-Orbit Torque and Anisotropic Magnetoresistance in a Topological Insulator Thin Film Attached to Ferromagnetic Layer

We investigate spin-charge conversion phenomena in hybrid structures of topological insulator (TI) thin films and magnetic insulators. We find an anisotropic inverse spin-galvanic effect (ISGE) that yields a highly tunable spin-orbit torque (SOT). Concentrating on the quasiballistic limit, we also predict a giant anisotropic magnetoresistance (AMR) at low dopings. These effects, which have no counterparts in thick TIs, depend on the simultaneous presence of the hybridization between the surface states and the in-plane magnetization. Both the ISGE and AMR exhibit a strong dependence on the magnetization and the Fermi level position and can be utilized for spintronics and SOT-based applications at the nanoscale.

cond-mat.mes-hall↗

arXiv2020

Rotating edge-field driven processing of chiral spin textures in racetrack devices

Topologically distinct magnetic structures like skyrmions, domain walls, and the uniformly magnetized state have multiple applications in logic devices, sensors, and as bits of information. One of the most promising concepts for applying these bits is the racetrack architecture controlled by electric currents or magnetic driving fields. In state-of-the-art racetracks, these fields or currents are applied to the whole circuit. Here, we employ micromagnetic and atomistic simulations to establish a concept for racetrack memories free of global driving forces. Surprisingly, we realize that mixed sequences of topologically distinct objects can be created and propagated over far distances exclusively by local rotation of magnetization at the sample boundaries. We reveal the dependence between the chirality of the rotation and the direction of propagation and define the phase space where the proposed procedure can be realized. The advantages of this approach are the exclusion of high current and field densities as well as its compatibility with an energy-efficient three-dimensional design.

cond-mat.mes-hall↗

arXiv2020

A Comprehensible Review: Magnonic Magnetoelectric Coupling in Ferroelectric/ Ferromagnetic Composites

Composite materials consisting of coupled magnetic and ferroelectric layers hold the promise for new emergent properties such as controlling magnetism with electric fields. Obviously, the interfacial coupling mechanism plays a crucial role and its understanding is the key for exploiting this material class for technological applications. This short review is focused on the magnonic-based magnetoelectric coupling that forms at the interface of a metallic ferromagnet with a ferroelectric insulator. After analyzing the physics behind this coupling, the implication for the magnetic, transport, and optical properties of these composite materials is discussed. Furthermore, examples for the functionality of such interfaces are illustrated by the electric field controlled transport through ferroelectric/ferromagnetic tunnel junctions, the electrically and magnetically controlled optical properties, and the generation of electromagnon solitons for the use as reliable information carriers.

cond-mat.mtrl-sci↗

arXiv2020

Multipolar, Polarization Shaped High Harmonic Generation by Intense Vector Beams

High harmonic generation (HHG) is a manifestation of the strongly nonlinear response of matter to intense laser fields and has, as the basis for coherent XUV sources a variety of applications. Recently, HHG from atoms in a phase and polarization structured laser was demonstrated and interpreted based on the transverse electric field component of the driving pulse. Here we point out that as dictated by Maxwell equations, such fields have a longitudinal component which in general has a fundamental influence on the charge dynamics. For instance, its interplay with the transversal field component enables endowing the emitted radiation locally with circular polarization and a defined polarity. It is shown that the time-dependent Stokes parameters defining the polarization state of HHG can be tuned by varying the waist of the driving field which in turn, changes the ratio between the longitudinal and transverse electric-field components of the driving laser. In addition, employing a multipole expansion of the produced harmonics exposes the specific multipolar character and the relation to the spatial structure of the driving field polarization states. The scheme proposed here allows a full polarization control of the emitted harmonics by only one driving laser. A tighter focusing of the driving pulse renders possible the emission of harmonics with both even and odd spatial symmetry. The underlying mechanism is due to the fundamental interplay between the transverse and longitudinal components of the laser's electromagnetic vector potential. The ratio between those components is controllable by just focusing the laser spot, pointing to an accessible tool for polarization and polarity control of the high harmonics.

physics.optics↗

arXiv2019

Steering magnonic dynamics and permeability at exceptional points in a parity-time symmetric waveguide

Tuning the low-energy magnetic dynamics is a key element in designing novel magnetic metamaterials, spintronic devices and magnonic logic circuits. This study uncovers a new, highly effective way of controlling the magnetic permeability via shaping the magnonic properties in coupled magnetic waveguides separated by current carrying spacer with strong spin-orbit coupling. The spin-orbit torques exerted on the waveguides leads to an externally tunable enhancement of magnetic damping in one waveguide and a decreased damping in the other, constituting so a magnetic parity-time (PT) symmetric system with emergent magnetic properties at the verge of the exceptional point where magnetic gains/losses are balanced. In addition to controlling the magnetic permeability, phenomena inherent to PT-symmetric systems are identified, including the control on magnon power oscillations, nonreciprocal magnon propagation, magnon trapping and enhancement as well as the increased sensitivity to magnetic perturbation and abrupt spin reversal. These predictions are demonstrated analytically and confirmed by full numerical simulations under experimentally feasible conditions. The position of the exceptional points and the strength of the spontaneous PT symmetry breaking can be tuned by external electric and/or magnetic fields. The roles of the intrinsic magnetic damping, and the possibility of an electric control via Dzyaloshinskii-Moriya interaction are exposed and utilized for mode dispersion shaping and magnon amplification and trapping. The results point to a new route to designing optomagnonic waveguides, traps, sensors, and circuits.

cond-mat.mes-hall↗

arXiv2019

Twisting and tweezing the spin wave: on vortices, skyrmions, helical waves, and the magnonic spiral phase plate

Spin waves are the low-energy excitations of magnetically ordered materials. They are key elements in the stability analysis of the ordered phase and have a wealth of technological applications. Recently, we showed that spin waves of a magnetic nanowire may carry a definite amount of orbital angular momentum components along the propagation direction. This helical, in addition to the chiral, character of the spin waves is related to the spatial modulations of the spin wave phase across the wire. It, however, remains a challenge to generate and control such modes with conventional magnetic fields. Here, we make the first proposal for a \textit{magnetic} spiral phase plate by appropriately synthesizing two magnetic materials that have different speeds of spin waves. It is demonstrated with full-numerical micromagnetic simulations that despite the complicated structure of demagnetization fields, a homogeneous spin wave passing through the spiral phase plate attains the required twist and propagates further with the desired orbital angular momentum. While excitations from the ordered phase may have a twist, the magnetization itself can be twisted due to internal fields and forms what is known as a magnetic vortex. We point out the differences between both types of magnetic phenomena and discuss their possible interaction.

cond-mat.mes-hall↗

arXiv2019

Ultrafast coupled charge and spin dynamics in strongly correlated NiO

Charge excitations across an electronic band gap play an important role in opto-electronics and light harvesting. In contrast to conventional semiconductors, studies of above-band-gap photoexcitations in strongly correlated materials are still in their infancy. Here we reveal the ultrafast dynamics controlled by Hund's physics in strongly correlated photo-excited NiO. By combining time-resolved two-photon photoemission experiments with state-of-the-art numerical calculations, an ultrafast ($\lesssim$ 10\,fs) relaxation due to Hund excitations and related photo-induced in-gap states are identified. Remarkably, the weight of these in-gap states displays long-lived coherent THz oscillations up to 2\,ps at low temperature. The frequency of these oscillations corresponds to the strength of the antiferromagnetic superexchange interaction in NiO and their lifetime vanishes as the Néel temperature is approached. Numerical simulations of a two-band $t$-$J$ model reveal that the THz oscillations originate from the interplay between local many-body excitations and long-range antiferromagnetic order.

cond-mat.str-el↗

arXiv2019

Electrical writing, deleting, reading, and moving of magnetic skyrmioniums in a racetrack device

A magnetic skyrmionium (also called 2$π$-skyrmion) can be understood as a skyrmion - a topologically non-trivial magnetic whirl - which is situated in the center of a second skyrmion with reversed magnetization. Here, we propose a new optoelectrical writing and deleting mechanism for skyrmioniums in thin films, as well as a reading mechanism based on the topological Hall voltage. Furthermore, we point out advantages for utilizing skyrmioniums as carriers of information in comparison to skyrmions with respect to the current-driven motion. We simulate all four constituents of an operating skyrmionium-based racetrack storage device: creation, motion, detection and deletion of bits. The existence of a skyrmionium is thereby interpreted as a '1' and its absence as a '0' bit.

cond-mat.str-el↗

arXiv2019

Entanglement balance of quantum $(e,2e)$ scattering processes

The theory of quantum information constitutes the functional value of the quantum entanglement, i.e., quantum entanglement is essential for high fidelity of quantum protocols, while fundamental physical processes behind the formation of quantum entanglement are less relevant for practical purposes. In the present work, we explore physical mechanisms leading to the emergence of quantum entanglement in the initially disentangled system. In particular, we analyze spin entanglement of outgoing electrons in a nonrelativistic quantum $(e,2e)$ collision on a target with one active electron. Our description exploits the time-dependent scattering formalism for typical conditions of scattering experiments, and contrary to the customary stationary formalism operates with realistic scattering states. We quantify the spin entanglement in the final scattering channel through the pair concurrence and express it in terms of the experimentally measurable spin-resolved $(e,2e)$ triple differential cross sections. Besides, we consider Bell's inequality and inspect the regimes of its violation in the final channel. We address both the pure and the mixed initial spin state cases and uncover kinematical conditions of the maximal entanglement of the outgoing electron pair. The numerical results for the pair concurrence, entanglement of formation, and violation of Bell's inequality obtained for the $(e,2e)$ ionization process of atomic hydrogen show that the entangled electron pairs indeed can be formed in the $(e,2e)$ collisions even with spin-unpolarized projectile and target electrons in the initial channel. The positive entanglement balance---the difference between entanglements of the initial and final electron pairs---can be measured in the experiment.

quant-ph↗

arXiv2019

Non-destructive Ultrafast Steering of Magnetic Vortex by Terahertz Pulses

Electric control of magnetic vortex dynamics in a reproducible way and on an ultrafast time scale is key element in the quest for efficient spintronic devices with low-energy consumption. To be useful the control scheme should ideally be swift, scalable, non-invasive, and resulting in reliable magnetic switching. Such requirements and in particular the reproducibility of altering the vortex chirality and/or polarity are not yet met by magnetic vortex switching via external magnetic fields, spin-polarized currents, spin waves, or laser pulses. Here we demonstrate a novel packaged-skyrmion mediated vortex switching process driven by a simple sequence of picosecond electrical field pulses via magneto-electric interactions. Both the vortex chirality and polarity show a well-defined reversal behaviour. The unambiguously repeated switching between four different magnetic vortex states provides an energy-efficient, highly localized and coherent control method for non-volatile magnetic vortex-based information storage and handling.

cond-mat.mes-hall↗