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INSTITUTE OF METAL PHYSICS OF NASU.
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HISTORY AND SCIENTIFIC RESULTS

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The department was founded in 1978 on the basis of the superconductivity laboratory which was organized in 1970. Since its foundation and up to 2012 the department had been headed by Prof. Dr. V.M. Pan.  Now the department is headed by Dr. O.A. Kordyuk, a corresponding member of the N.A.S. of Ukraine.

From 1970 to 1987, the department had carried out fundamental research in physics of the low-temperature superconductors: 

  • The relation of the critical temperature, Tc, and the upper critical field, Hc2, with composition and structure of the material, as well as with the properties of the electron and phonon spectra had been found experimentally. New superconducting compound, Nb3Si, with high Tc had been synthesized for the first time. This result had been repeated by the United States and Japan only several years later. (V.M. Pan, A.G. Popov).
  • The physical basis for synthesis of new class of superconducting materials—the deformed nanostructured alloys with "directionally-aligned" superfine defects with high critical current density in high magnetic fields—had been developed. (V.M. Pan, Yu.I. Beletskii).
  • The physical basis for the diffusion formation process of layers of Nb3Sn with high density non-dissipative supercurrent and minimal losses in an alternating electromagnetic field had been developed. The results of this research had allowed to develop an effective technology for production of the superconducting material for a current-carrying coaxial cable, and the technology for manufacturing of bulk microwave resonators (V.F. Flis, V. F. Taborov, V.M. Pan).
  • Within a joint experiment with USA, a prototype of Nb3Sn-cable for power lines had been created. The Ukrainian line had shown the current-carrying ability of an order of magnitude higher than the line made by American team (V.M. Pan, Yu.I. Belitskii, V.S. Flis, G.A. Klimenko).

For the development and study of low-temperature superconductors with high current-carrying ability V.M. Pan and Yu.I. Belitskii in 1982 were awarded with the State Prize of the Ukrainian SSR. The results of the researches are summarized in the monograph by V.M. Pan, V.G. Prokhorov, and A.S. Shpigel "Metal Physics of Superconductors" (1984). 

Since 1987, the researchers of the department have been focused in study of high-temperature superconductors (HTSC). The electromagnetic properties and problems of electrodynamics had been extensively researched taking into account actual structure of these layered anisotropic compounds.

  • It has been shown that new "electrostatic" mechanism of magnetic vortex pinning by electrically charged defects (oxygen vacancies and cores of edge dislocations), which is related to the energy difference of the Coulomb screening in normal and superconducting states, is effective in high-temperature superconductors with low concentration of a charge carriers and low Fermi energy (E.A. Pashitskii, K.G Tretiachenko, V.M. Pan).
  • The technique of growing of high quality HTSC single crystals and original techniques for their investigation have been developed. It has been found that the anomalous temperature dependence of the surface resistance of HTSC single crystal YBa2Cu3 O7-b in the superconducting state, measured at 10 GHz frequency, is caused by a decrease of charge carrier concentration in thin surface layer of 1-3 nm (V.F. Taborov, V. F. Tarasov).
  • It has been shown for the first time that the pinning of the magnetic flux vortices in high quality single crystals of YBa2Cu3O7-b is caused by point defects and two-dimensional planar defects (i.e. oxygen vacancies and twin domains boundaries). Anomalous nonmonotonic character of orientation and magnetic field (peak effect) dependences of critical current density in these single crystals is a consequence of dimensional crossover from two-dimensional pinning on point defects to three-dimensional pinning by increasing the external field, which is connected to the dispersion of the elastic bending modulus C44 (k) of the vortex lattice. Studying the dynamics of the vortex lattice motion has allowed to establish the mechanisms of dissipation in both slow hopping thermal activated creep and rapid flux flow at which the dissipation occurs under the classical mechanism that was described as the motion of an elastically deformable continuum in a viscous medium (V.F. Soloviov, V.M. Pan).
  • The mechanisms of pinning and depinning of vortices in moderately anisotropic HTSC (YBa2Cu3O7-b) with the same linear defects (dislocations or heavy-ion irradiation tracks) have been found and the possibility of formation of partially depinned vortices near the surface has been shown (A.L. Kasatkin). The new "dislocation" model for the motion of vortices along the low-angle boundaries in HTSC films of YBa2Cu3O7-b has been developed. That was the first model that explained the behavior of the critical current density depending on the misorientation angle of neighboring domains (A.L. Kasatkin, V.M. Pan).
  • A study of the electrodynamics of superconductors has been performed. The study included: an investigation of mechanisms of pinning of the vortex lines and a mechanism of destruction of non-dissipative current state; solving the problem of summation of elementary pinning forces in superconductors with varying degrees of defects, the study of the dynamic features of the mixed state (A.L. Kasatkin).
  • The technological basis for the synthesis of superconducting thin films by electron-beam evaporation and pulse laser deposition methods has been developed (V.S. Flis).
  • The study of the processes of HTSC films growth of the compound YBa2Cu3O7-b, obtained by pulse laser deposition has been performed. A strong correlation between the modes of synthesis and microstructure of the deposited samples, which allows to control the mechanism of nucleation and HTSC films growth, has been found (V.G. Prokhorov, V.I Matsui).
  • Anisotropy of bulk pinning force of the vortex lines in different directions of the external magnetic field with respect to the film surface has been found. It has been shown that this effect is determined by the characteristics of the microstructure and, to a lesser extent, associated with the anisotropy of the crystal lattice of HTSC (V.G. Prokhorov, G.G. Kaminskii).
  • The current-voltage characteristics and their first derivatives for HTSC films in a dynamic mixed state have been studied. The areas of the viscous flow of magnetic flux have been found on the current-voltage characteristics close to the transition temperature. Anomalous dependence of the of the flux flow resistance on magnetic field can be explained in the framework of a theoretical model that allows the formation of channels of easy vortex lines slip along the grain boundaries. This conclusion is also supported by the two-peak dependence of the immaginary part on the magnetic susceptibility on temperature (V.G.Prokhorov, M.A. Kuznetsov).
  • The methods of computer simulation of nucleation and growth of HTSC films depending on the deposition conditions have been developed. (K. G. Tretiachenko).
In 2005, the group of Dr. A.A. Kordyuk, which has been focused on experimental research of the electronic structure of high-temperature superconductors, has joined the department. The following main results has been obtained in this direction: 
  • The spin-fluctuation nature of the electron scattering and superconducting pairing in high-temperature superconductors has been experimentally proved (A.A. Kordyuk).
  • It has been shown that the pseudogap in HTSC cuprates is a result of an incommensurate spin density wave (A. A. Kordyuk, A. I. Plyushchay).
  • A number of new iron based superconductors have been investigated, their electronic structure has been identified and a clear relation of this structure with the superconducting transition has been revealed (D.V. Evtushinsky, A.A. Kordyuk).
An effect of the photoemission gating of spin-polarized surface states in topological insulators has been discovered (A. A. Kordyuk, D.V. Evtushinsky, A. I. Plyushchay).