Mehrdad Elyasi 교수

We theoretically explore nonlinearities of ferromagnets in microwave cavities in the classical and quantum regimes and assess the resources for quantum information, i.e., fluctuation squeezing and bipartite entanglement. The (semi)classical analysis of the anharmonic oscillator (Duffing) model for the Kittel mode when including all other magnon modes, reveals chaotic and limit-cycle phases that do not survive in quantum calculations. However, magnons with nonzero wave numbers that are driven by

The intrinsic nonlinearities of the spin dynamics in condensed matter systems give rise to a rich phenomenology that can be strongly affected by topology. Here, we study formation of magnonic solitons in the topologically nontrivial band gap of a spin lattice realization of the Haldane model, in both static and dynamic (Floquet) regimes. We consider nonlinearities caused by magnetic crystalline anisotropy and magnon-magnon interactions. We find soliton formation power thresholds as a function of

Unconventional computing schemes based on bistable systems (``Ising spins'') may supersede conventional computing paradigms. The ``magnon parametron'' is an Ising spin that forms as a result of parametric excitation of a ferromagnetic particle by microwaves beyond a certain threshold. This Ising spin becomes unstable at a second threshold power at which a high-frequency telegraph noise emerges. We explain the experimentally observed stochastic switching (``p-bit'' characteristics) at room temper

We have proposed a method to synchronize multiple spin-transfer torque oscillators based on spin pumping, inverse spin Hall, and spin Hall effects. The proposed oscillator system consists of a series of nano-magnets in junction with a normal metal with high spin-orbit coupling, and an accumulative feedback loop. We conduct simulations to demonstrate the effect of modulated charge currents in the normal metal due to spin pumping from each nano-magnet. We show that the interplay between the spin H

We present a theory of the nonlinear spin Seebeck effect (SSE) in a ferromagnetic nanowire at cryogenic temperatures. We adopt a microscopic quantum noise model based on a collection of two-level systems. At certain positions of Pt detectors to the wire, the transverse SSE changes sign as a function of temperature and/or temperature gradient. On the other hand, the longitudinal SSE does not show significant nonlinearities even far outside the regime of validity of linear response theory.

Telegraph noise caused by frequent switching of the magnetization in small magnetic devices has become a useful resource for probabilistic computing. Conventional theories have been based on a linearization of the fluctuations at the extrema of the magnetic free energy. We show theoretically that the nonlinearities, specifically four-magnon scatterings, reduce the equilibrium fluctuation amplitude of the magnetization as well as the switching frequencies between local minima via the decay of the

Magnets are interesting materials for classical and quantum information technologies. However, the short decoherence and dephasing times that determine the scale and speed of information networks severely limit the appeal of employing the ferromagnetic resonance. Here we show that the lifetime and coherence of the uniform Kittel mode can be enhanced by three-magnon interaction-induced mixing with the long-lived magnons at the minima of the dispersion relation. Analytical and numerical calculatio

We have considered the effect of different spin-orbit interaction mechanisms on the process of demagnetization under the influence of short-pulse lasers. All-optical magnetization reversal of perpendicularly magnetized thin films can occur if there are sufficient strong spin-Hall, skew scattering, and Rashba interactions. In the presence of spin-orbit interactions, the transient charge currents provide the generation of transverse-spin currents and accumulations, which eventually exert spin-tran

We propose two approaches to cloak the spin waves (magnons) by investigating magnetization dynamics. One approach is based on a spatially inhomogeneous anisotropic magnetic moment tensor. The other mechanism is using a spatially inhomogeneous anisotropic gyromagnetic factor tensor and an inhomogeneous external magnetic field. For both approaches, the damping tensor is also inhomogeneous and anisotropic. The magnetic characteristic functions of the magnetic materials have been theoretically deriv

Telegraph noise caused by frequent switching of the magnetization in small magnetic devices has become a useful resource for probabilistic computing. Conventional theories have been based on a linearization of the fluctuations at the extrema of the magnetic free energy. We show theoretically that the non-linearities, specifically four-magnon scatterings, reduce the equilibrium fluctuation amplitude of the magnetization as well as the switching frequencies between local minima via the decay of th

We have proposed a method for magnetization reversal of individual sites of a 2 by 2 matrix of perpendicularly magnetized dots by common current excitation. The spin-polarized current signal consists of a dc-biased ac part followed by a pure dc one. The amplitude of the dc and ac parts of the current, as well as the phase and duration of the ac current, determine the reversal sites through the magnetostatic interaction among the dots. We show that the individual selectivity in magnetization reve

A novel micro-electro-mechanical (MEM) based non-volatile memory (NVM) is proposed. The storage principle is based on Lorentz's transduction, utilizing long-range motion of a non-anchored element which has current carrying sliding contact with a conductive path. Position of the moving element indicates the stored data in the multi-bit cell. Data is written in the cell with displacing the moving element by Lorentz's force, is read by utilizing differential port resistances, and is held by adhesio

We have proposed an approach for reversing magnetization of individual sites of a 2 by 2 matrix of perpendicularly magnetized dots by common excitation with a spin-polarized current. The spin-polarized current signal is formed of a dc-biased ac part followed by a dc section. In such a matrix, where all the parameters and initial conditions are the same, a spatial and temporal interaction and interference is needed to separate the individual dot dynamics in the phase space. By controlled modulati

The 'magnon parametron' is a ferromagnetic particle that is parametrically excited by microwaves in a cavity. Above a certain threshold of the microwave power, a bistable steady state emerges that forms an effective Ising spin. We calculate the dynamics of the magnon parametron as a function of microwave power, applied magnetic field and temperature for the interacting magnon system, taking into account thermal and quantum fluctuations. We predict three dynamical phases, viz. a stable Ising spin

The large arrays of magnetic dots are the basis of magnonic crystals and bit patterned media. Resonance behaviors of densely packed magnetic arrays have been a subject of recent intensified research for their applications in microwave technology or signal transfer. Structural or magnetization non-uniformities in magnonic crystals lead to the appearance of defect modes, resulting in the modification of the magnon band-structure. It has been demonstrated experimentally that the state of a vortex m