Alexander Kovalev, Leading Researcher.

E-mail: kovalev@ilt.kharkov.ua
Tel. +38 (0572) 330 85 39.

Was born in Ulan–Ude (USSR) in 1945.
Graduated from Kharkov State University in1967.
PhD Phys & Math, Kharkov State University, 1975.

DrS (1989) and Professor degrees (2001) in Theoretical physics in ILTPE. Now is the Leading Researcher in ILTP and the professor in Kharkov National University. Area of expertise is the soliton dynamics of magnetically ordered and elastic media, nonlinear phenomena in dynamical systems, mathematical aspects of nonlinear mechanics. Is a co-author of 2 monographs, 3 reviews and 140 articles. Lecturer activity: lecturing on theoretical mechanics and nonlinear physics at Kharkov National University. Foreign activity: scientific visitor in Regensburg (Germany), Bayreuth (Germany), Paris (France), Canberra (Australia) and Aston (UK) universities during the years 1994-2004.

Main current research interests: theory of nonlinear structures and waves in solid state.

(I) Investigation of nonlinear surface waves during last years includes studying of nonlinear surface shear waves (It was demonstrated the importance of a spatial dispersion of elastic media and criteria of stability for NSSW and surface shear solitons were formulated); the SSS were studied as a general problem of 2D and 3D solitons in media with acoustic spectrum and the special asyptotical procedures for them were proposed; the different surface Rayleigh solitons with a stationary profile were investigated near perfect surface and surface covered with thin film or monolayer. In the last cases the nonlinear non-local ID evolution equations were derived and their unusual soliton solutions were obtained. Recently some special problems for nonlinear elastic surface waves were investigated: propagation of envelope SRS, properties of "gap" SRS near the corrugated surface, propagation of exotic solitons with combined polarization in nonlinear elastic plates with effective nonlinear dispersion, derivation of nonlinear evolution equations for nonlinear elastic systems with restricted geometry and second-order nonlinearity. Some results were obtained for nonlinear elastic waves and solitons near the surface in the incommensurate state.

(II) Nonlinear dynamics of magnets is a traditional field of interest: the specific nonlinear excitations - "magnetic solitons" were studying and the novel conception of magnetic soliton as a bound state of magnons was formulated. In this area some important results were obtained: the exact solutions for ID solitons in ferro- and anti-feromagnets; exact many-solitons solutions in ID FM; numerical solutions for many-dimensional magnetic solitons; 2D skirmions and vortices in FM. Later some specific phenomena of nonlinear magnetic structure and dynamics was investigated: magnetic solitons in thin films and nonlinear surface spin waves, magnetic frustrations in HTSC, complicated topological solitons in AFM with dislocations, dynamical and topological solitons and internal modes in quasi 2D essentially discrete FM, exotic magnetic solitons, magnetic structure and dynamics of FM/AFM perfect and imperfect interfaces. Recently the main interests are concentrated on the structure and dynamics of magnetic vortices, vortex pairs and their interaction with spin waves and external fields, magnetic vortices in magnetic nanodots.

(III) Special problems of nonlinear mechanic and mathematical aspects of solitonic theory were studied including: some asymptotic techniques for envelope solitons in ID- 2D- and finite size systems; Hirota transformation, N-solitons solutions and spin-wave spectrum in the presence of domain walls; exact solutions for incommensurated systems; the connection of solitons in the systems with distributed parameters with their quasi-soliton analogous in the systems with finite number degrees of freedom. Recently some problems of nonlinear optical pulse propagation in fibers were intensively studied. Another "optical activity" is connected with propagation of nonlinear optical beams through spatial periodic media and properties of optical "supersolitons”. The particular attention is devoted to investigation of "gap-solitons" and their discrete analogs. (Researches were provided in collaboration with the group members – M. Bogdan, Ya. Prilepskyi).

 Main publications:

1. A.M.Kosevich, B.A.Ivanov, A.S.Kovalev, Nonlinear waves of magnetization. Dynamical and topological solitons, Kiev, Naukova Dumka (1983).

2. A.M.Kosevich, B.A.Ivanov, A.S.Kovalev, Magnetic solitons: A new type of collective excitations in magnetically ordered systems, Sov.Sci.Rev., A6,161-260 (1985).

3. A.M.Kosevich, B.A.Ivanov, A.S.Kovalev, Magnetic solitons, Phys.Rep., v.194, N3/4, 117-238 (1990).

4. A.M.Kosevich, A.S.Kovalev, Introduction in nonlinear physical mechanics, Kiev, Naukova dumka (1989).

Main last publications:

1. C.Eckl, J.Schollmann, A.P.Mayer, A.S.Kovalev, G.A.Maugin, On the stability of surface acoustic pulse trains in coated elastic media, Wave motion, 34, 35-49 (2001).

2. T.Kamppeter, S.A.Leonel, F.G.Mertens, M.E.Gouvea, A.S.T.Pires, A.S.Kovalev, Topological and dynamival excitations in a classical 2D easy-axis Heisenberg model, Eur.Phys.J., B21, 93-102 (2001).

3. A.S.Kovalev, S.Komineas, F.G.Mertens, Scattering of vortex pairs in 2D easy-plane ferromagnets, Eur. Phys. J.B 25, 89-100 (2002).

4. A.S.Kovalev, A.P.Mayer, C.Eckl, G.A.Maugin, Solitary Rayleigh waves in the presence of surface nonlinearity, Phys. Rev. E 66, 036615 (2002).

5. A.S.Kovalev, F.G.Mertens, H.J.Schnitzer, Cycloidal vortex motion in easy-plane ferromagnets due to interaction with spin waves, Eur. Phys. J. B 33, 133-145 (2003).

6. A.P.Mayer, A.S.Kovalev, Envelope solitons of acoustic plate modes and surface waves, Phys. Rev. E 67, 066603-1-14 (2003).