arXiv subjects

J. Berakdar

Publications and source records attributed to J. Berakdar.

At least 73 records · Page 4Linked to original sources

arXiv2012

Magnetoelectric coupling in a ferroelectric/ferromagnetic chain revealed by ferromagnetic resonance

Understanding the multiferroic coupling is one of the key issues in the feld of multiferroics. As shown here theoretically, the ferromagnetic resonance (FMR) renders possible an access to the magnetoelectric coupling coefficient in composite multiferroics. This we evidence by a detailed analysis and numerical calculations of FMR in an unstrained chain of BaTiO3 in the tetragonal phase in contact with Fe, including the effect of depolarizing field. The spectra of the absorbed power in FMR are found to be sensitive to the orientation of the interface electric polarization and to an applied static electric field. Here we propose a method for measuring the magnetoelectric coupling coefficient by means of FMR.

cond-mat.mtrl-sci↗

arXiv2012

Time-evolution of excitations in normal Fermi liquids

We inspect the initial and the long time evolution of excitations a Fermi liquids by analyzing the time behavior of the electron spectral function. Focusing on the short-time limit we study the electron-boson model for the homogenous electron gas and apply the first order (in boson propagator) cumulant expansion of the electron Green's function. In addition to a quadratic decay in time upon triggering the excitation, we identify non-analytic terms in the time expansion similar to those found in the Fermi edge singularity phenomenon. We also demonstrate that the exponential decay in time in the long-time limit is inconsistent with the GW approximation for the self-energy. The background for this is the Paley-Wiener theorem of complex analysis. To reconcile with the Fermi liquid behavior an inclusion of higher order diagrams (in the screened Coulomb interaction) is required.

cond-mat.str-el↗

arXiv2012

Nonlinear anomalous Hall effect and negative magnetoresistance in a system with random Rashba field

We predict two spin-dependent transport phenomena in two-dimensional electron systems, which are induced by spatially fluctuating Rashba spin-orbit interaction. When the electron gas is magnetized, the random Rashba interaction leads to the anomalous Hall effect. An example of such a system is a narrow-gap magnetic semiconductor-based symmetric quantum well. We show that the anomalous Hall conductivity reveals a strongly nonlinear dependence on the magnetization, decreasing exponentially at large spin density. We also show that electron scattering from a fluctuating Rashba field in a two-dimensional nonmagnetic electron system leads to a negative magnetoresistance arising solely due to spin-dependent effects.

cond-mat.mes-hall↗

arXiv2012

Theoretical proposal for the dynamical control of the nonlinear optical response frequency

We propose theoretically a method for the control of the frequency of the nonlinear optical response of a model nonlinear medium driven by an electric field and suggest an experimental realization on the basis of isotropic LiF, or NaCl crystals and pulsed Nd glass laser. The theoretical background of the proposed optical control is the nonlinear resonance and the resonance overlapping which is typical for nonlinear systems. It is shown that by a proper choice of the parameters of the applied pulses a diffusive growth of the oscillation amplitude can be achieved resulting in a controlled switching of the system's frequency. The maximum frequency of the nonlinear response is identified to be proportional to the intensity of the applied noise. An experimental suggestion for particular materials is proposed.

physics.optics↗

arXiv2012

Semi-classical approximation for the second harmonic generation in nanoparticles

Second harmonic generation by spherical nanoparticles is a non-local optical process that can also be viewed as the result of the non-linear response of the thin interface layer. The classical electrodynamic description, based e.g. on the non-linear Mie theory, entails the knowledge of the dielectric function and the surface non-linear optical susceptibility, both quantities are usually assumed to be predetermined, for instance from experiment. We propose here an approach based on the semi-classical approximation for the quantum sum-over-states expression that allows to capture the second-order optical process from first principles. A key input is the electronic density, which can be obtained from effective single particle approaches such as the density-functional theory in the local density implementation. We show that the resulting integral equations can be solved very efficiently rendering thus the treatment of macroscopic systems. As an illustration we present numerical results for the magic Na2869 cluster.

cond-mat.mes-hall↗

arXiv2012

Attosecond tracking of light absorption and refraction in fullerenes

The collective response of matter is ubiquitous and widely exploited, e.g. in plasmonic, optical and electronic devices. Here we trace on an attosecond time scale the birth of collective excitations in a finite system and find distinct new features in this regime. Combining quantum chemical computation with quantum kinetic methods we calculate the time-dependent light absorption and refraction in fullerene that serve as indicators for the emergence of collective modes. We explain the numerically calculated novel transient features by an analytical model and point out the relevance for ultra-fast photonic and electronic applications. A scheme is proposed to measure the predicted effects via the emergent attosecond metrology.

physics.atm-clus↗

arXiv2011

Indirect Interaction of Magnetic Domain Walls

We calculate the electron-mediated exchange interaction between two domain walls in magnetic wires. This corresponds to the equilibrium regime and, therefore, the interaction can be additionally controlled by an electric current. The exchange interaction is long ranged and oscillates as a function of the distance between the walls. It also depends oscillatory on the polarization angle of the walls, having the maximum value for collinear polarization.

cond-mat.mes-hall↗

arXiv2011

Photo-induced spin filtering in a double quantum dot

We investigate the spin-resolved electron dynamics in a double quantum dot driven by ultrafast asymmetric electromagnetic pulses. Using a analytical model we show that applying an appropriate pulse sequence allows to control coherently the spin degree of freedom on the femtosecond time scale. It can be achieved that the spin-up state is localized in a selected quantum dot while the spin-down state remains in the other dot. We show that this photo-induced spin-dependent separation can be maintained for a desired period of time.

cond-mat.mes-hall↗

arXiv2011

Chaotic spin-dependent electron dynamics in a field-driven double dot potential

We study the nonlinear classical dynamics of an electron confined in a double dot potential and subjected to a spin-orbit coupling and a constant external magnetic field. It is shown that due to the spin orbit coupling, the energy can be transferred from the spin to the orbital motion. This naturally heats up the orbital motion which, due to the presence of the separatrix line in the phase space of the system, results in a motion of the electron between the dots. It is shown that depending on the strength of the spin orbit coupling and the energy of the system, the electronic orbital motion undergoes a transition from the regular to the chaotic regime.

nlin.CD↗

arXiv2011

Superatom molecular orbitals: a new type of long-lived electronic states

We present ab initio calculations of the quasiparticle decay times in a Buckminsterfullerene based on the many-body perturbation theory. A particularly lucid representation arises when the broadening of the quasiparticle states is plotted in the angular momentum and energy coordinates. In this representation the main spectroscopic features of the fullerene consist of two occupied nearly parabolic bands, and delocalized plane-wave-like unoccupied states with a few long-lived electronic states (the superatom molecular orbitals, SAMOs) embedded in the continuum of Fermi-liquid states. SAMOs have been recently uncovered experimentally by M. Feng, J. Zhao, and H. Petek [Science 320, 359 (2008)] using scanning tunneling spectroscopy. The present calculations offer an explanation of their unusual stability and unveil their long-lived nature making them good candidates for applications in the molecular electronics. From the fundamental point of view these states illustrate a concept of the Fock-space localization [B. L. Altshuler, Y. Gefen, A. Kamenev, and L. S. Levitov, Phys. Rev. Lett. 78, 2803 (1997)] with properties drastically different from the Fermi-liquid excitations.

cond-mat.mes-hall↗

arXiv2011

Spin-orbital phase synchronization in the magnetic field-driven electron dynamics in a double quantum dot

We study the dynamics of an electron confined in a one-dimensional double quantum dot in the presence of driving external magnetic fields. The orbital motion of the electron is coupled to the spin dynamics by spin orbit interaction of the Dresselhaus type. We derive an effective time-dependent Hamiltonian model for the orbital motion of the electron and obtain a synchronization condition between the orbital and the spin dynamics. From this model we deduce an analytical expression for the Arnold tongue and propose an experimental scheme for realizing the synchronization of the orbital and spin dynamics.

nlin.CD↗

arXiv2011

On the initial stage of quasiparticle decay

The initial stages of the quasiparticle decay in a Fermi liquid are governed by a time-scale distinct from the scattering rates as derived from the Fermi golden rule approach. We show that the initial decay is nonexponential and that it is determined by the zeroth spectral moment of the electron self-energy. We analyzed numerically a number of approximations for the self-energy by comparing with exact configuration interaction calculations for small finite system with fragmented states. A numerically simple approach for computing the spreading of the quasiparticle states for large systems is devised.

cond-mat.str-el↗

arXiv2011

Nonlinear dynamics of two coupled nano-electromechanical resonators

As a model of coupled nano-electromechanical resonantors we study two nonlinear driven oscillators with an arbitrary coupling strength between them. Analytical expressions are derived for the oscillation amplitudes as a function of the driving frequency and for the energy transfer rate between the two oscillators. The nonlinear restoring forces induce the expected nonlinear resonance structures in the amplitude-frequency characteristics with asymmetric resonance peaks. The corresponding multistable behavior is shown to be an efficient tool to control the energy transfer arising from the sensitive response to small changes in the driving frequency. Our results imply that the nonlinear response can be exploited to design precise sensors for mass or force detection experiments based on nano-electromechanical resonators.

nlin.CD↗

arXiv2011

Two-photon driven nonlinear dynamics and entanglement of an atom in a non uniform cavity

In this paper we study the dynamics in the general case for a Tavis Cummings atom in a non-uniform cavity. In addition to the dynamical Stark shift, the center-of-mass motion of the atom and the recoil effect are considered in both - the weak and the strong cavity atom coupling regimes. It is shown that the spatial motion of the atom inside the cavity in the resonant case leads to a transition between topologically different solutions. This effect is manifested by a singularity in the inter-level transition spectrum. In the non-resonant case, the spatial motion of the atom leads to a switching of the spin orientation. In both effects, the key factor is the relation between the values of the Stark shift and the cavity field coupling constant. We also investigate the entanglement of an atom in the cavity with the radiation field. It is shown that the entanglement between the atom and the field, usually quantified in terms of purity, decreases with increasing the Stark shift.

quant-ph↗

arXiv2011

Chaotic dynamics and spin correlation functions in a chain of nanomagnets

We study a chain of coupled nanomagnets in a classical approximation. We show that the infinitely long chain of coupled nanomagnets can be equivalently mapped onto an effective one-dimensional Hamiltonian with a fictitious time-dependent perturbation. We establish a connection between the dynamical characteristics of the classical system and spin correlation time. The decay rate for the spin correlation functions turns out to depend logarithmically on the maximal Lyapunov exponent. Furthermore, we discuss the non-trivial role of the exchange anisotropy within the chain.

cond-mat.mes-hall↗

arXiv2011

Thermal entanglement and efficiency of the quantum Otto cycle for the su(1,1) Tavis-Cummings system

The influence of the dynamical Stark shift on the thermal entanglement and the efficiency of the quantum Otto cycle is studied for the su(1,1) Tavis-Cummings system. It is shown that the degree of the thermal entanglement becomes larger as the dynamical Stark shift increases. In contrast, the efficiency of the Otto cycle is degraded with an increase of the values of dynamical Stark shift. Expressions for the efficiency coefficient are derived. Using those expressions we identify the maximal efficiency of the quantum Otto cycle from the experimentally measured values of the dynamical Stark shift

quant-ph↗

arXiv2010

Polarization and magnetization dynamics of a field-driven multiferroic structure

We consider a multiferroic chain with a linear magnetoelectric coupling induced by the electrostatic screening at the ferroelectric/ferromagnet interface. We study theoretically the dynamic ferroelectric and magnetic response to external magnetic and electric fields by utilizing an approach based on coupled Landau- Khalatnikov and finite-temperature Landau-Lifshitz-Gilbert equations. Additionally, we compare with Monte Carlo calculations. It is demonstrated that for material parameters corresponding to BaTiO3/Fe the polarization and the magnetization are controllable by external magnetic and electric fields respectively.

cond-mat.mtrl-sci↗

arXiv2010

Stochastic heating of a molecular nanomagnet

We study the excitation dynamics of a single molecular nanomagnet by static and pulsed magnetic fields. Based on a stability analysis of the classical magnetization dynamics we identify analytically the fields parameters for which the energy is stochastically pumped into the system in which case the magnetization undergoes diffusively and irreversibly a large angle deflection. An approximate analytical expression for the diffusion constant in terms of the fields parameters is given and assessed by full numerical calculations.

nlin.CD↗