Tetiana Leontievna Linnik

National Academy of Sciences of Ukraine | ISP · Department of Theoretical Physics

Phonons and magnons are prospective information carriers to substitute the transfer of charge in nanoscale communication devices. Our ability to manipulate them at the nanoscale and with ultimate speed is examined by ultrafast acoustics and femtosecond optomagnetism, which use ultrashort laser pulses for generation and detection of the correspondin...

Using the path-integral approach, we have developed a general solution of the problem of a noise-induced escape or transition of the overdamped one-dimensional potential system at time scales of the order of dynamic relaxation time. The results strongly differ from those obtained before by other methods. Computer simulations confirm the validity of...

We demonstrate a variety of precessional responses of the magnetization to ultrafast optical excitation in nanolayers of galfenol (Fe,Ga), which is a ferromagnetic material with large saturation magnetization and enhanced magnetostriction. The particular properties of galfenol, including cubic magnetic anisotropy and weak damping, allow us to detec...

We demonstrate a variety of precessional responses of the magnetization to ultrafast optical excitation in nanolayers of Galfenol (Fe,Ga), which is a ferromagnetic material with large saturation magnetization and enhanced magnetostriction. The particular properties of Galfenol, including cubic magnetic anisotropy and weak damping, allow us to detec...

We demonstrate spin pumping, i.e. the generation of a pure spin current by precessing magnetization, without application of microwave radiation commonly used in spin pumping experiments. We use femtosecond laser pulses to simultaneously launch the magnetization precession in each of two ferromagnetic layers of a Galfenol-based spin valve and monito...

We demonstrate spin pumping, i.e. the generation of a pure spin current by precessing magnetization, without application of microwave radiation commonly used in spin pumping experiments. We use femtosecond laser pulses to simultaneously launch the magnetization precession in each of two ferromagnetic layers of a Galfenol-based spin valve and monito...

Picosecond duration compressive and shear phonon wavepackets injected into (311) GaAs slabs transform after propagation through �1 mm into chirped acoustic pulses with a frequency increasing in time due to phonon dispersion. By probing the temporal optical response to coherent phonons in a near surface layer of the GaAs slab, we show that phonon ch...

Dynamical strain generated upon excitation of a metallic film by a femtosecond laser pulse may become a versatile tool enabling control of magnetic state of thin _lms and nanostructures via inverse magnetostriction on a picosecond time scale. Here we explore two alternative approaches to manipulate magnetocrystalline anisotropy and excite magnetiza...

Dynamical strain generated upon excitation of a metallic film by a femtosecond laser pulse may become a versatile tool enabling control of magnetic state of thin films and nanostructures via inverse magnetostriction on a picosecond time scale. Here we explore two alternative approaches to manipulate magnetocrystalline anisotropy and excite magnetiz...

Ultrafast optical excitation of a metal ferromagnetic film results in a modification of the magnetocrystalline anisotropy and induces the magnetization precession. We consider two main contributions to these processes: an effect of noncoherent phonons, which modifies the temperature dependent parameters of the magnetocrystalline anisotropy and cohe...

The theoretical results are presented showing that strain-induced anisotropy of graphene spectrum gives rise to the valley currents under the illumination by normally incident light. The currents of the two graphene valleys are mutually compensated providing zero net electric current. The magnitude and direction of the valley currents are determine...

Coherent high-amplitude precession of the magnetization and spin waves with frequencies up to 40 GHz are generated by injecting picosecond compressive and shear acoustic pulses into nanometer-sized galfenol (Fe81Ga19) films. The magnetization modulation is due to the picosecond inverse magnetostrictive effect. The oscillations of the magnetization...

By means of a metal opto-acoustic transducer we generate quasi-longitudinal and quasi-transverse picosecond strain pulses in a (311)-GaAs substrate and monitor their propagation by picosecond acoustic interferometry. By probing at the sample side opposite to the transducer the signals related to the compressive and shear strain pulses can be separa...

Quasi-longitudinal and quasi-transverse picosecond strain pulses injected into a ferromagnetic (311) (Ga,Mn)As film induce dynamical shear strain in the film, thereby modulating the magnetic anisotropy and inducing resonant precession of the magnetization at a frequency ~10 GHz. The modulation of the out-of-plane magnetization component by the quas...

Based on the symmetry properties of the graphene lattice, we derive the effective Hamiltonian of graphene under spatially nonuniform acoustic and optical strains. Comparison with the published results of the first-principles calculations allows us to determine the values of some Hamiltonian parameters, and suggests the validity of the derived Hamil...

A theoretical model of the coherent precession of magnetization excited by a picosecond acoustic pulse in a ferromagnetic semiconductor layer of (Ga,Mn)As is developed. The short strain pulse injected into the ferromagnetic layer modifies the magnetocrystalline anisotropy resulting in a tilt of the equilibrium orientation of magnetization and subse...

A source of nanometer wavelength, transverse-polarized, sound waves based on stimulated emission of phonons in a semiconductor superlattice inside an acoustic cavity and pumped by a low-average power nanosecond pulsed laser is described. The experimental evidence for sound laser (saser) action in our device is a superlinear increase in emitted acou...

We demonstrate that mismatch of the piezoelectric coefficients of the layers of a superlattice structure gives rise to the drastic enhancement of electron-phonon interaction for resonant acoustic phonons, propagating at small angle to the superlattice axis and having frequency close to 2πns/d, where s is sound velocity, d is superlattice period, a...

In this report we demonstrate stimulated terahertz acoustic phonon emission from a superlattice under hopping electron transport. Stimulated emission occurs as a result of population‐inverted electron distribution with respect to the phonon‐assisted interwell electron transitions as well as feed‐back due to phonon confinement. The confinement is a...

We show that piezoelectric electron-phonon coupling in multilayered structures is strongly enhanced for resonant phonons propagating close to the normal to the layers and having wavevector close to integers of 2π/d, where d is the structure period. This is a direct result of the mismatch of the piezoelectric parameters in distinct layers of the str...

We report measurements of acoustic phonon emission from a weakly coupled AlAs/GaAs superlattice (SL) under vertical electron transport. The phonons were detected using superconducting bolometers. A peak (resonance) was observed in emission parallel to the SL growth axis when the electrical energy drop per SL period matched the energy of the first S...

We show that mismatch of the piezoelectric parameters between layers of multiple-quantum well structures leads to modification of the electron-phonon interaction. In particular, short-wavelength phonons propagating perpendicular to the layers with wavevector close to $2\pi n/d$, where $d$ is the period of the structure, induce a strong smoothly-var...

We find the complete general solution of the noise-induced escape/transition problem on time scales less than or order of the relaxation time. The theory is checked in simulations. The most interesting unsolved problems are: (i) calculation of the first-order correction and matching of our results with those by Shneidman obtained for larger time-sc...

This paper presents theoretical results on stimulated and spontaneous monochromatic terahertz acoustic phonon emission in layered semiconductor nanostructures. In addition, this study discusses their relation with recent experimental findings and possible applications for optoelectronics and materials science.

We consider by means of the optimal fluctuation method the initial stage of the evolution of the noise-induced escape through various types of boundaries, especially concentrating on two types of the boundary - the wall and the boundary of the basin of attraction. We show in both cases that, if the damping is small enough, then the escape flux evol...

We demonstrate that in nanostructures an additional mechanism of electron-acoustic phonon interaction has to be considered along with traditional mechanisms. It was addressed previously by Pekar for bulk crystals with extremely high dielectric permittivity. The additional coupling is due to macroscopic electrical potential which is caused by modula...

We consider an electron-acoustic phonon coupling mechanism associated with the dependence of crystal dielectric permittivity on the strain (the so-called Pekar mechanism) in nanostructures characterized by strong confining electric fields. The efficiency of Pekar coupling is a function of both the absolute value and the spatial distribution of the...

Noise-induced escape from the metastable part of potential is considered on time scales preceding the formation of quasiequilibrium within that part of the potential. It is shown that, counterintuitively, the escape flux may depend exponentially strongly, and in a complicated manner, on time and friction.

In the problem of the activation energy for a noise-induced transition over a finite given time in an arbitrary overdamped one-dimensional potential system, we find and classify all extremal paths and provide a simple algorithm to explicitly select which is the most probable transition path (MPTP). The activation energy is explicitly expressed in q...

In the problem of the activation energy for a noise-induced transition over a finite given time in an arbitrary overdamped one-dimensional potential system, we find and classify all extremal paths and provide a simple algorithm to explicitly select which is the most probable transition path (MPTP). The activation energy is explicitly expressed in q...

We demonstrate that doped superlattices in the hopping conduction regime can be used for efficient generation of high-frequency coherent acoustic phonons. The phonons that can be generated in actual finite-length superlattice structures lay at the edge of the phonon miniband and have vanishingly small radiation losses. This causes onset of the phon...

In this work we consider the theory of high-frequency phonon generation in a weakly coupled doped semiconductor superlattice. Electric bias, applied to such a superlattice, destroys the electron minibands, creates electron states localized in the individual quantum wells, and forms population inversion between these states. An electric current occu...

For electrically biased superlattices exhibiting the effect of phonon instability (see paper I), we analyze the nonlinear problem of high-frequency acoustic phonon generation. We develop a theory treating self-consistently phonon generation and electron transport through the superlattice. We find that the dominant mechanism associated with the stea...

Noise-induced escape from the metastable part of a potential is considered on time scales preceding the formation of quasiequilibrium within that part of the potential. It is shown that, counterintuitively, the escape flux may then depend exponentially strongly, and in a complicated manner, on time and friction. (c) 2001 American Institute of Physi...

We prove rigorously and demonstrate in simulations that, for a potential system staying initially at the bottom of a well, the escape flux over the barrier grows on times of the order of a period of eigenoscillation in a stepwise manner, provided that friction is small or moderate. If the initial state is not at the bottom of the well, then, typica...

We prove rigorously and demonstrate in simulations that, for a potential system staying initially at the bottom of a well, the escape flux over the barrier grows on times of the order of a period of eigenoscillation in a stepwise manner, provided that friction is small or moderate. If the initial state is not at the bottom of the well, then, typica...

Escape from a metastable potential is considered on time-scales less than are needed for the creation of quasi-equilibrium within the well. It is shown that the escape flux may then depend exponentially strongly, and in a complicated way, on friction and time. .

We studied a biased superlattice and revealed a considerable current response to irradiation by non-equilibrium acoustic phonons with an effective temperature on the order of a few Kelvins. We discuss two phonon source-superlattice configurations, for which the current response is caused by either interwell or intrawell electron transitions. We hav...

Noise-induced escape from a metastable potential is considered on time-scales preceding the formation of quasi-equilibrium within the metastable part of the potential. It is shown that the escape flux may then depend exponentially strongly, and in a complicated manner, on time and friction. .

In cubic semiconductors the hole-mass ratio is small, which makes it possible to use the zero light-hole-mass limit. It was found that variational methods in this popular limit are not necessary to solve the Luttinger equation and not only the entire energy spectrum for the bound states of an acceptor and the eigenfunctions, including in momentum s...

In this work we analyze conditions of generation of high frequency coherent acoustic phonons in a biased semiconductor superlattice. We show that the electron perpendicular transport provides the electron population inversion for interwell phonon-assisted transitions and generation of phonons propagating along the superlattice axis. The generation...

In cubic semiconductors the light hole and heavy hole masses ratio is small. That is why there were some attempts to describe these crystals by the model of zero light hole mass. But in all papers investigations were limited by the ground state. We took a more general approach which yields an exact analytical solution for all acceptor states and es...

It is shown that the shape of a hole magnetic polaron in a semimagnetic semiconductor with the sphalerite structure is anisotropic: The polaron is strongly oblate in the direction of its magnetic moment. When the anisotropy of the hole spectrum is taken into account, the properties of the polaron depend on the orientation of its spin with respect t...

In this work we consider the theory of sound amplification under the hopping perpendicular transport in a semiconductor superlattice. It is shown that phonons propagating close to the axis of super lattice demonstrate high values of the increment, exceeding the ra.tes of the phonon scattering on natural isotopes. Effects, restricting the value of i...