2014: Associate Prof. Alexei Oreshko (chair of solid state physics) defended his Dr. Sciences thesis on "Anisotropic and Interference Effects in Resonance Diffraction on Synchrotron Radiation"

In April 2014, Associate Prof. Alexei Oreshko (Chair of Solid State Physics) defended his Dr. Sciences thesis on "Anisotropic and Interference Effects in Resonance Diffraction on Synchrotron Radiation."

In his Dr.Sci. thesis A.Oreshko develops new method for studying the properties of condensed matter, based on the diffraction of X-rays with energies close to the absorption edges of the atoms of the substance.

In terms of diffraction resonance scattering anisotropy and polarization dependence leads to the appearance of "forbidden" reflections missing in the diffraction away from the absorption edges of the atoms of the substance because of the system symmetry, but near the absorption edges occur when the incident radiation energy is close to the required for electron transition from inner-shell electrons in the outer shells of the unoccupied state or to the continuum. Of particular interest are "forbidden" reflections caused by the presence of several contributions of different nature in the scattering anisotropy. Spectral intensity of the reflection has a complex structure and interference carries unique information about the splitting of the electronic states in the substance.

However, currently existing theory of resonant X-ray scattering allows only a qualitative description of effects that occur when there is only one anisotropic factor influencing the resonant scattering. Therefore, the purpose of studies which form the basis of the Dr.Sci. thesis was to develop theoretical methods for the study of X-ray synchrotron radiation resonant diffraction in locally anisotropic media in the presence of several anisotropic factors.

Studies conducted in the thesis suggest that the method developed resonance spectroscopy of "forbidden" reflections to solve the problem of distorted studies of electron and phonon states in locally anisotropic media and opens prospects for the study of structural, magnetic and electronic properties of locally anisotropic media inaccessible to other methods.