Alexey Dyachenko | Altai State Pedagogical Academy (original) (raw)

Alexey Dyachenko

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Papers by Alexey Dyachenko

Research paper thumbnail of Two successive spin transitions in a wide range of pressure and coexistence of high- and low-spin states in clinoferrosiliteFeSiO3

Research paper thumbnail of Electronic structure and magnetic state of transuranium metals under pressure

Journal of Physics: Condensed Matter, 2010

Electronic structure of bcc Np, fcc Pu, Am, and Cm pure metals under pressure has been investigat... more Electronic structure of bcc Np, fcc Pu, Am, and Cm pure metals under pressure has been investigated employing the LDA+U method with spin-orbit coupling (LDA+U +SO). Magnetic state of the actinide ions was analyzed in both LS and jj coupling schemes to reveal the applicability of corresponding coupling bases. It was demonstrated that whereas Pu and Am are well described within the jj coupling scheme, Np and Cm can be described appropriately neither in {mσ}, nor in {jmj } basis, due to intermediate coupling scheme realizing in these metals that requires some finer treatment. The LDA+U +SO results for the considered transuranium metals reveal bands broadening and gradual 5f electron delocalization under pressure.

Research paper thumbnail of Electrical resistivity of pure transuranium metals under pressure

Journal of Nuclear Materials, 2011

Research paper thumbnail of Temperature and concentration dependences of the electrical resistivity for alloys of plutonium with americium under normal conditions

Journal of Experimental and Theoretical Physics, 2010

The temperature and concentration dependences of the electrical resistivity for alloys of ameri c... more The temperature and concentration dependences of the electrical resistivity for alloys of ameri cium with plutonium are analyzed in terms of the multiband conductivity model for binary disordered sub stitution type alloys. For the case of high temperatures (T > Θ D , Θ D is the Debye temperature), a system of self consistent equations of the coherent potential approximation has been derived for the scattering of con duction electrons by impurities and phonons without any constraints on the interaction intensity. The defi nitions of the shift and broadening operator for a single electron level are used to show qualitatively and quan titatively that the pattern of the temperature dependence of the electrical resistivity for alloys is determined by the balance between the coherent and incoherent contributions to the electron-phonon scattering and that the interference conduction electron scattering mechanism can be the main cause of the negative tem perature coefficient of resistivity observed in some alloys involving actinides. It is shown that the great values of the observed resistivity may be attributable to interband transitions of charge carriers and renormalization of their effective mass through strong s-d band hybridization. The concentration and temperature depen dences of the resistivity for alloys of plutonium and americium calculated in terms of the derived conductivity model are compared with the available experimental data.

Research paper thumbnail of LDA+DMFT study of magnetic transition and metallization in CoO under pressure

JETP Letters, 2012

In this work we report results of magnetic and spectral properties calculation for paramagnetic p... more In this work we report results of magnetic and spectral properties calculation for paramagnetic phase of CoO at ambient and high pressures performed within the LDA+DMFT method combining local density approximation (LDA) with dynamical mean-eld theory (DMFT). From our results CoO at ambient pressure is a charge transfer insulator in the high-spin t 5 2g e 2 g con guration. The energy gap is continuously decreased, and nally a transition into metallic state occurs with the increase of pressure that is consistent with experimental behavior of electrical resistivity. Notably, the metal-insulator transition in CoO is found to be accompanied by the high-spin to low-spin (HS{LS) transition in agreement with XES data. The metal-insulator transition is orbital selective in the t2g states of cobalt only, whereas the eg states become metallic after the spin transition at higher pressures.

Research paper thumbnail of Two successive spin transitions in a wide range of pressure and coexistence of high- and low-spin states in clinoferrosiliteFeSiO3

Research paper thumbnail of Electronic structure and magnetic state of transuranium metals under pressure

Journal of Physics: Condensed Matter, 2010

Electronic structure of bcc Np, fcc Pu, Am, and Cm pure metals under pressure has been investigat... more Electronic structure of bcc Np, fcc Pu, Am, and Cm pure metals under pressure has been investigated employing the LDA+U method with spin-orbit coupling (LDA+U +SO). Magnetic state of the actinide ions was analyzed in both LS and jj coupling schemes to reveal the applicability of corresponding coupling bases. It was demonstrated that whereas Pu and Am are well described within the jj coupling scheme, Np and Cm can be described appropriately neither in {mσ}, nor in {jmj } basis, due to intermediate coupling scheme realizing in these metals that requires some finer treatment. The LDA+U +SO results for the considered transuranium metals reveal bands broadening and gradual 5f electron delocalization under pressure.

Research paper thumbnail of Electrical resistivity of pure transuranium metals under pressure

Journal of Nuclear Materials, 2011

Research paper thumbnail of Temperature and concentration dependences of the electrical resistivity for alloys of plutonium with americium under normal conditions

Journal of Experimental and Theoretical Physics, 2010

The temperature and concentration dependences of the electrical resistivity for alloys of ameri c... more The temperature and concentration dependences of the electrical resistivity for alloys of ameri cium with plutonium are analyzed in terms of the multiband conductivity model for binary disordered sub stitution type alloys. For the case of high temperatures (T > Θ D , Θ D is the Debye temperature), a system of self consistent equations of the coherent potential approximation has been derived for the scattering of con duction electrons by impurities and phonons without any constraints on the interaction intensity. The defi nitions of the shift and broadening operator for a single electron level are used to show qualitatively and quan titatively that the pattern of the temperature dependence of the electrical resistivity for alloys is determined by the balance between the coherent and incoherent contributions to the electron-phonon scattering and that the interference conduction electron scattering mechanism can be the main cause of the negative tem perature coefficient of resistivity observed in some alloys involving actinides. It is shown that the great values of the observed resistivity may be attributable to interband transitions of charge carriers and renormalization of their effective mass through strong s-d band hybridization. The concentration and temperature depen dences of the resistivity for alloys of plutonium and americium calculated in terms of the derived conductivity model are compared with the available experimental data.

Research paper thumbnail of LDA+DMFT study of magnetic transition and metallization in CoO under pressure

JETP Letters, 2012

In this work we report results of magnetic and spectral properties calculation for paramagnetic p... more In this work we report results of magnetic and spectral properties calculation for paramagnetic phase of CoO at ambient and high pressures performed within the LDA+DMFT method combining local density approximation (LDA) with dynamical mean-eld theory (DMFT). From our results CoO at ambient pressure is a charge transfer insulator in the high-spin t 5 2g e 2 g con guration. The energy gap is continuously decreased, and nally a transition into metallic state occurs with the increase of pressure that is consistent with experimental behavior of electrical resistivity. Notably, the metal-insulator transition in CoO is found to be accompanied by the high-spin to low-spin (HS{LS) transition in agreement with XES data. The metal-insulator transition is orbital selective in the t2g states of cobalt only, whereas the eg states become metallic after the spin transition at higher pressures.

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