arXiv subjects

Jamal Berakdar

Publications and source records attributed to Jamal Berakdar.

102 records · Page 6Linked to original sources

arXiv2010

Spin-dependent pump current and noise in an adiabatic quantum pump based on domain walls in a magnetic nanowire

We study the pump current and noise properties in an adiabatically modulated magnetic nanowire with double domain walls (DW). The modulation is brought about by applying a slowly oscillating magnetic and electric fields with a controllable phase difference. The pumping mechanism resembles the case of the quantum dot pump with two-oscillating gates. The pump current, shot noise, and heat flow show peaks when the Fermi energy matches with the spin-split resonant levels localized between the DWs. The peak height of the pump current is an indicator for the lifetime of the spin-split quasistationary states between the DWs. For sharp DWs, the energy absorption from the oscillating fields results in side-band formations observable in the pump current. The pump noise carries information on the correlation properties between the nonequilibrium electrons and the quasi-holes created by the oscillating scatterer. The ratio between the pump shot noise and the heat flow serves as an indicator for quasi-particle correlation.

cond-mat.mes-hall↗

arXiv2009

Charge and spin Hall effect in graphene with magnetic impurities

We point out the existence of finite charge and spin Hall conductivities of graphene in the presence of a spin orbit interaction (SOI) and localized magnetic impurities. The SOI in graphene results in different transverse forces on the two spin channels yielding the spin Hall current. The magnetic scatterers act as spin-dependent barriers, and in combination with the SOI effect lead to a charge imbalance at the boundaries. As indicated here, the charge and spin Hall effects should be observable in graphene by changing the chemical potential close to the gap.

cond-mat.mtrl-sci↗

arXiv2009

Electrically controlled persistent spin currents at the interface of multiferroic oxides

We predict the appearance of a persistent spin current in a two-dimensional electron gas formed at the interface of multiferroic oxides with a transverse helical magnetic order. No charge current is generated. This is the result of an effective spin-orbit coupling generated by the topology of the oxide local magnetic moments. The effective coupling and the generated spin current depend linearly on the magnetic spiral helicity which, due to the magneto-electric coupling, is tunable by a transverse electric field offering thus a new mean for the generation of electrically controlled persistent spin currents.

cond-mat.mes-hall↗

arXiv2009

Multiferroic oxides-based flash-memory and spin-field-effect transistor

We propose a modified spin-field-effect transistor fabricated in a two dimensional electron gas (2DEG) formed at the surface of multiferroic oxides with a transverse helical magnetic order. The topology of the oxide local magnetic moments induces a resonant momentum-dependent effective spin-orbit interaction acting on 2DEG. We show that spin polarization dephasing is strongly suppressed which is crucial for functionality. The carrier spin precession phase depend linearly on the magnetic spiral helicity. The latter is electrically controllable by virtue of the magento-electric effect. We also suggest a flash-memory device based on this structure.

cond-mat.mtrl-sci↗

arXiv2009

Localized magnetic states in biased bilayer and trilayer graphene

We study the localized magnetic states of impurity in biased bilayer and trilayer graphene. It is found that the magnetic boundary for bilayer and trilayer graphene presents the mixing features of Dirac and conventional fermion. For zero gate bias, as the impurity energy approaches the Dirac point, the impurity magnetization region diminishes for bilayer and trilayer graphene. When a gate bias is applied, the dependence of impurity magnetic states on the impurity energy exhibits a different behavior for bilayer and trilayer graphene due to the opening of a gap between the valence and the conduction band in the bilayer graphene with the gate bias applied. The magnetic moment and the corresponding magnetic transition of the impurity in bilayer graphene are also investigated.

cond-mat.mes-hall↗

arXiv2009

Dynamical magnetoelectric effects induced by the Dzyaloshinskii-Moriya interaction in multiferroics

We study the dynamical interplay between ferroelectricity and magnetism in a multiferroic with a helical magnetic order. We show that the dynamical exchange-striction induces a biquadratic interaction between the spins and transverse phonons resulting in quantum fluctuations of the spontaneous ferroelectric polarization $\mathbf{P}$ in the ferroelectric phase. The hybridization between the spin wave and the fluctuation of the electric polarization leads to low-lying transverse phonon modes. Those are perpendicular to $\mathbf{P}$ and to the helical spins at small wave vector but then turn parallel to $\mathbf{P}$ at a wave vector close to the magnetic modulation vector. For helical magnetic structure, the spin chirality which determines the direction of $\mathbf{P}$, also possesses a long-range order. Due to the dynamical Dzyaloshiskii-Moriya interaction, the spin-chirality is strongly coupled to the spin fluctuation which implies an on-site inversion of the spin-chirality in the ordered spin-1/2 system and results in a finite scattering intensity of polarized neutrons from a cycloidal helimagnet.

cond-mat.str-el↗

arXiv2009

Electromagnetic Pulse Driven Spin-dependent Currents in Semiconductor Quantum Rings

We investigate the non-equilibrium charge and spin-dependent currents in a quantum ring with a Rashba spin orbit interaction (SOI) driven by two asymmetric picosecond electromagnetic pulses. The equilibrium persistent charge and persistent spin-dependent currents are investigated as well. It is shown that the dynamical charge and the dynamical spin-dependent currents vary smoothly with a static external magnetic flux and the SOI provides a SU(2) effective flux that changes the phases of the dynamic charge and the dynamic spin-dependent currents. The period of the oscillation of the total charge current with the delay time between the pulses is larger in a quantum ring with a larger radius. The parameters of the pulse fields control to a certain extent the total charge and the total spin-dependent currents. The calculations are applicable to nano-meter rings fabricated in heterojuctions of III-V and II-VI semiconductors containing several hundreds electrons.

cond-mat.mes-hall↗

arXiv2009

Magnetotransport through graphene spin valves

We present a theoretical study on the spin-dependent transport through a spin valve consisting of graphene sandwiched between two magnetic leads with an arbitrary orientation of the lead magnetization. No gate voltage is applied. Using Keldysh's nonequilibrium Green's function method we show that, in absence of external magnetic fields, the current-voltage curves are nonlinear. Around zero bias the differential conductance versus bias voltage possesses a strong dip. The zero-bias anomaly in the tunnel magnetoresistance (TMR) is affected strongly by the leads spin polarization. Depending on the value of the bias voltage TMR exhibits a behavior ranging from an insulating to a metallic-type. In presence of a static external magnetic field the differential conductance and TMR as a function of the bias voltage and the strength of the magnetic field show periodic oscillations due to Landau-level crossings. We also inspect the effects of the temperature and the polarization degrees on the differential conductance and TMR.

cond-mat.mes-hall↗

arXiv2008

Photo-induced, non-equilibrium spin and charge polarization in quantum rings

We investigate the spin-dependent dynamical response of a quantum ring with a spin-orbit interaction upon the application of linearly polarized, picosecond, asymmetric electromagnetic pulses. The oscillations of the generated dipole moment are sensitive to the parity of the occupation number in the ring and to the strength of the spin-orbit coupling. It is shown how the associated emission spectrum can be controlled via the pulse strength or a gate voltage. In addition, we inspect how a static magnetic flux can modify the non-equilibrium dynamics. In presence of the spin-orbit interaction and for a paramagnetic ring, the applied pulse results in a spin-split, non-equilibrium local charge density. The resulting temporal spin polarization is directed perpendicular to the light-pulse polarization axis and oscillates periodically with the frequency of the spin-split charge density. The spin-averaged non-equilibrium charge density possesses a left-right symmetry with respect to the pulse polarization axis. The calculations presented here are applicable to nano-meter rings fabricated in heterojuctions of III-V and II-VI semiconductors containing several hundreds electrons.

cond-mat.mes-hall↗

arXiv2008

Temperature dependent magnetization dynamics of magnetic nanoparticles

Recent experimental and theoretical studies show that the switching behavior of magnetic nanoparticles can be well controlled by external time-dependent magnetic fields. In this work, we inspect theoretically the influence of the temperature and the magnetic anisotropy on the spin-dynamics and the switching properties of single domain magnetic nanoparticles (Stoner-particles). Our theoretical tools are the Landau-Lifshitz-Gilbert equation extended as to deal with finite temperatures within a Langevine framework. Physical quantities of interest are the minimum field amplitudes required for switching and the corresponding reversal times of the nanoparticle's magnetic moment. In particular, we contrast the cases of static and time-dependent external fields and analyze the influence of damping for a uniaxial and a cubic anisotropy.

cond-mat.other↗

arXiv2001

Many-body scattering theory of electronic systems

This work reviews recent advances in the analytical treatment of the continuum spectrum of correlated few-body non-relativistic Coulomb systems. The exactly solvable two-body problem serves as an introduction to the non-separable three-particle system. For the latter case we discuss the existence of an approximate separability of the long and the short-range dynamics which is exposed in an appropriately chosen curvilinear coordinates. The three-body wave functions of the long-ranged part of the Hamiltonian are derived and methods are presented to account approximately for the short-ranged dynamics. Furthermore, we present a generalization of the methods employed for the derivation of the three-body wave functions to the scattering states of $N$ charged particles. To deal with thermodynamic properties of finite systems we develop and discuss a recent Green function methodology designed for the non-perturbative regime. In addition, we give a brief account on how thermodynamic properties and critical phenomena can be exposed in finite interacting systems.

math-ph↗

arXiv1999

Probing the spin polarization in ferromagnets

The emission of correlated electrons from an itinerant ferromagnet following the impact of a polarized electron beam is analyzed in terms of irreducible tensorial parameters that can be measured. Under favorable conditions, specified in this work, these parameters are related to the spin polarization in the ferromagnet. The formal results are illustrated by numerical studies of the polarized electron pair emission from a Fe(110) surface and a novel technique for the investigation of magnetic properties of ferromagnets is suggested.

cond-mat.str-el↗