Oleg Zakharov - Academia.edu (original) (raw)

Papers by Oleg Zakharov

Research paper thumbnail of Band Structures of CdS and CdSe at High Pressure

Indirect energy gaps of NaCl-structured CdS and CdSe are measured using absorption spectroscopy t... more Indirect energy gaps of NaCl-structured CdS and CdSe are measured using absorption spectroscopy to approximately 55 GPa and 42 GPa, respectively. The gaps shift linearly with pressure, and their pressure dependence is in generally good agreement with previous measurements to 16 GPa. Also, band calculations using pseudopotentials and density functional theory are conducted on CdS as a function of pressure. The shift in the energy gap of CdS with pressure (dE_gap/dP), is experimentally determined to be -5.7× 10-3 eV/GPa, in good agreement with the theoretical calculation of -5.6 × 10-3 eV/GPa. The pressure dependence of the gap of CdSe is measured to be -4.0(2) × 10-3 eV/GPa, while previous theoretical work yielded -6.0 × 10-3 eV/GPa. Relative to a previous experimental result on CdSe, our measured shift is in considerably closer agreement with theory. The energy gap in both materials is indirect throughout the pressure range of these measurements. There is also no compression-induced change in the location in k-space of the valence band maxima for either the experimental or theoretical results. In contrast to previous inferences for CdS, the gap appears to remain from the L point to the X point up to our maximum pressure. Based on a simple linear extrapolation of our data, we estimate the metallization pressures of NaCl-structured CdS and CdSe.

Research paper thumbnail of Quasiparticle band structures of six II-VI compounds: ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe

Research paper thumbnail of Ab initio calculations of the pressure-induced structural phasetransitions for four II-VI compounds

Research paper thumbnail of Band structure of CdS and CdSe at high pressure

Research paper thumbnail of Phonon softening and superconductivity in tellurium under pressure

The phonon dispersion and the electron-phonon interaction for the beta\betabeta-Po and the bcc high pre... more The phonon dispersion and the electron-phonon interaction for the beta\betabeta-Po and the bcc high pressure phases of tellurium are computed with density-functional perturbation theory. Our calculations reproduce and explain the experimentally observed pressure dependence of the superconducting critical temperature (T$_{\rm c}$) and confirm the connection between the jump in T$_{\rm c}$ and the structural phase transition. The phonon contribution to the free energy is shown to be responsible for the difference in the structural transition pressure observed in low and room temperature experiments.

Research paper thumbnail of bold {ital Ab initio}} calculations of the pressure-induced structural phase transitions for four II-VI compounds

Research paper thumbnail of Dynamical screening at the metal-semiconductor interface and excitonic superconductivity

Research paper thumbnail of Ab initio calculations of the pressure-induced structural phase transitionsfor four II-VI compounds

Research paper thumbnail of Band Structures of CdS and CdSe at High Pressure

Indirect energy gaps of NaCl-structured CdS and CdSe are measured using absorption spectroscopy t... more Indirect energy gaps of NaCl-structured CdS and CdSe are measured using absorption spectroscopy to approximately 55 GPa and 42 GPa, respectively. The gaps shift linearly with pressure, and their pressure dependence is in generally good agreement with previous measurements to 16 GPa. Also, band calculations using pseudopotentials and density functional theory are conducted on CdS as a function of pressure. The shift in the energy gap of CdS with pressure (dE_gap/dP), is experimentally determined to be -5.7× 10-3 eV/GPa, in good agreement with the theoretical calculation of -5.6 × 10-3 eV/GPa. The pressure dependence of the gap of CdSe is measured to be -4.0(2) × 10-3 eV/GPa, while previous theoretical work yielded -6.0 × 10-3 eV/GPa. Relative to a previous experimental result on CdSe, our measured shift is in considerably closer agreement with theory. The energy gap in both materials is indirect throughout the pressure range of these measurements. There is also no compression-induced change in the location in k-space of the valence band maxima for either the experimental or theoretical results. In contrast to previous inferences for CdS, the gap appears to remain from the L point to the X point up to our maximum pressure. Based on a simple linear extrapolation of our data, we estimate the metallization pressures of NaCl-structured CdS and CdSe.

Research paper thumbnail of Calculated structural and electronic properties of CdSe under pressure

Research paper thumbnail of Theory of structural, electronic, vibrational, and superconducting properties of high-pressure phases of sulfur

Research paper thumbnail of Phonon softeting and superconductivity in tellurium under pressure

The phonon dispersion and the electron-phonon interaction for the β-Po and the bcc high pressure ... more The phonon dispersion and the electron-phonon interaction for the β-Po and the bcc high pressure phases of tellurium have been computed (F. Mauri, O. Zakharov, S. de Gironcoli, S. G. Louie, and M. L. Cohen, Phys. Rev. Lett. 77, 1151 (1996)) using density-functional perturbation theory and the local density approximation. The results of the calculation reproduce and explain the experimentally observed pressure dependence of the superconducting critical temperature (T_c) and confirm the connection between the jump in Tc and the structural phase transition. In particular, the pressure dependence of Tc is shown to be primarily determined by the pressure dependence of the phonon frequencies. Moreover, the phonon contribution to the free energy is found to be responsible for the difference in the structural transition pressure observed in low and room temperature experiments.

Research paper thumbnail of Quasiparticle band structures of six II-VI compounds: ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe

Research paper thumbnail of Phonon Softening and Superconductivity in Tellurium under Pressure

Physical Review Letters, 1996

The phonon dispersion and the electron-phonon interaction for the β-Po and the bcc high pressure ... more The phonon dispersion and the electron-phonon interaction for the β-Po and the bcc high pressure phases of tellurium are computed with density-functional perturbation theory. Our calculations reproduce and explain the experimentally observed pressure dependence of the superconducting critical temperature ( Tc) and confirm the connection between the jump in Tc and the structural phase transition. The phonon contribution to the free energy is shown to be responsible for the difference in the structural transition pressure observed in low and room temperature experiments.

Research paper thumbnail of Ab initio calculations of the pressure-induced structural phasetransitions for four II-VI compounds

Research paper thumbnail of Phonon Softening and Superconductivity in Tellurium under Pressure

Physical Review Letters, 1996

The phonon dispersion and the electron-phonon interaction for the beta\betabeta-Po and the bcc high pre... more The phonon dispersion and the electron-phonon interaction for the beta\betabeta-Po and the bcc high pressure phases of tellurium are computed with density-functional perturbation theory. Our calculations reproduce and explain the experimentally observed pressure dependence of the superconducting critical temperature (T$_{\rm c}$) and confirm the connection between the jump in T$_{\rm c}$ and the structural phase transition. The phonon contribution to the free energy is shown to be responsible for the difference in the structural transition pressure observed in low and room temperature experiments.

Research paper thumbnail of Band structure of CdS and CdSe at high pressure

Research paper thumbnail of Dynamical screening at the metal - semiconductor interface and excitonic superconductivity

Journal of Physics-condensed Matter, 1997

We examine the possibility of excitonic superconductivity at a metal - semiconductor interface. A... more We examine the possibility of excitonic superconductivity at a metal - semiconductor interface. An ab initio RPA calculation of the screened Coulomb electron - electron interaction is performed for the silicon - jellium multilayer model. The superconducting kernel for this multilayered system is found to be positive in the whole frequency range considered. We show that the inclusion of local field effects does not change the sign of the kernel and thus does not enhance the excitonic mechanism.

Research paper thumbnail of Phonon softening and superconductivity in tellurium under pressure

The phonon dispersion and the electron-phonon interaction for the beta\betabeta-Po and the bcc high pre... more The phonon dispersion and the electron-phonon interaction for the beta\betabeta-Po and the bcc high pressure phases of tellurium are computed with density-functional perturbation theory. Our calculations reproduce and explain the experimentally observed pressure dependence of the superconducting critical temperature (T$_{\rm c}$) and confirm the connection between the jump in T$_{\rm c}$ and the structural phase transition. The phonon contribution to the free energy is shown to be responsible for the difference in the structural transition pressure observed in low and room temperature experiments.

Research paper thumbnail of bold {ital Ab initio}} calculations of the pressure-induced structural phase transitions for four II-VI compounds

Research paper thumbnail of Band Structures of CdS and CdSe at High Pressure

Indirect energy gaps of NaCl-structured CdS and CdSe are measured using absorption spectroscopy t... more Indirect energy gaps of NaCl-structured CdS and CdSe are measured using absorption spectroscopy to approximately 55 GPa and 42 GPa, respectively. The gaps shift linearly with pressure, and their pressure dependence is in generally good agreement with previous measurements to 16 GPa. Also, band calculations using pseudopotentials and density functional theory are conducted on CdS as a function of pressure. The shift in the energy gap of CdS with pressure (dE_gap/dP), is experimentally determined to be -5.7× 10-3 eV/GPa, in good agreement with the theoretical calculation of -5.6 × 10-3 eV/GPa. The pressure dependence of the gap of CdSe is measured to be -4.0(2) × 10-3 eV/GPa, while previous theoretical work yielded -6.0 × 10-3 eV/GPa. Relative to a previous experimental result on CdSe, our measured shift is in considerably closer agreement with theory. The energy gap in both materials is indirect throughout the pressure range of these measurements. There is also no compression-induced change in the location in k-space of the valence band maxima for either the experimental or theoretical results. In contrast to previous inferences for CdS, the gap appears to remain from the L point to the X point up to our maximum pressure. Based on a simple linear extrapolation of our data, we estimate the metallization pressures of NaCl-structured CdS and CdSe.

Research paper thumbnail of Quasiparticle band structures of six II-VI compounds: ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe

Research paper thumbnail of Ab initio calculations of the pressure-induced structural phasetransitions for four II-VI compounds

Research paper thumbnail of Band structure of CdS and CdSe at high pressure

Research paper thumbnail of Phonon softening and superconductivity in tellurium under pressure

The phonon dispersion and the electron-phonon interaction for the beta\betabeta-Po and the bcc high pre... more The phonon dispersion and the electron-phonon interaction for the beta\betabeta-Po and the bcc high pressure phases of tellurium are computed with density-functional perturbation theory. Our calculations reproduce and explain the experimentally observed pressure dependence of the superconducting critical temperature (T$_{\rm c}$) and confirm the connection between the jump in T$_{\rm c}$ and the structural phase transition. The phonon contribution to the free energy is shown to be responsible for the difference in the structural transition pressure observed in low and room temperature experiments.

Research paper thumbnail of bold {ital Ab initio}} calculations of the pressure-induced structural phase transitions for four II-VI compounds

Research paper thumbnail of Dynamical screening at the metal-semiconductor interface and excitonic superconductivity

Research paper thumbnail of Ab initio calculations of the pressure-induced structural phase transitionsfor four II-VI compounds

Research paper thumbnail of Band Structures of CdS and CdSe at High Pressure

Indirect energy gaps of NaCl-structured CdS and CdSe are measured using absorption spectroscopy t... more Indirect energy gaps of NaCl-structured CdS and CdSe are measured using absorption spectroscopy to approximately 55 GPa and 42 GPa, respectively. The gaps shift linearly with pressure, and their pressure dependence is in generally good agreement with previous measurements to 16 GPa. Also, band calculations using pseudopotentials and density functional theory are conducted on CdS as a function of pressure. The shift in the energy gap of CdS with pressure (dE_gap/dP), is experimentally determined to be -5.7× 10-3 eV/GPa, in good agreement with the theoretical calculation of -5.6 × 10-3 eV/GPa. The pressure dependence of the gap of CdSe is measured to be -4.0(2) × 10-3 eV/GPa, while previous theoretical work yielded -6.0 × 10-3 eV/GPa. Relative to a previous experimental result on CdSe, our measured shift is in considerably closer agreement with theory. The energy gap in both materials is indirect throughout the pressure range of these measurements. There is also no compression-induced change in the location in k-space of the valence band maxima for either the experimental or theoretical results. In contrast to previous inferences for CdS, the gap appears to remain from the L point to the X point up to our maximum pressure. Based on a simple linear extrapolation of our data, we estimate the metallization pressures of NaCl-structured CdS and CdSe.

Research paper thumbnail of Calculated structural and electronic properties of CdSe under pressure

Research paper thumbnail of Theory of structural, electronic, vibrational, and superconducting properties of high-pressure phases of sulfur

Research paper thumbnail of Phonon softeting and superconductivity in tellurium under pressure

The phonon dispersion and the electron-phonon interaction for the β-Po and the bcc high pressure ... more The phonon dispersion and the electron-phonon interaction for the β-Po and the bcc high pressure phases of tellurium have been computed (F. Mauri, O. Zakharov, S. de Gironcoli, S. G. Louie, and M. L. Cohen, Phys. Rev. Lett. 77, 1151 (1996)) using density-functional perturbation theory and the local density approximation. The results of the calculation reproduce and explain the experimentally observed pressure dependence of the superconducting critical temperature (T_c) and confirm the connection between the jump in Tc and the structural phase transition. In particular, the pressure dependence of Tc is shown to be primarily determined by the pressure dependence of the phonon frequencies. Moreover, the phonon contribution to the free energy is found to be responsible for the difference in the structural transition pressure observed in low and room temperature experiments.

Research paper thumbnail of Quasiparticle band structures of six II-VI compounds: ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe

Research paper thumbnail of Phonon Softening and Superconductivity in Tellurium under Pressure

Physical Review Letters, 1996

The phonon dispersion and the electron-phonon interaction for the β-Po and the bcc high pressure ... more The phonon dispersion and the electron-phonon interaction for the β-Po and the bcc high pressure phases of tellurium are computed with density-functional perturbation theory. Our calculations reproduce and explain the experimentally observed pressure dependence of the superconducting critical temperature ( Tc) and confirm the connection between the jump in Tc and the structural phase transition. The phonon contribution to the free energy is shown to be responsible for the difference in the structural transition pressure observed in low and room temperature experiments.

Research paper thumbnail of Ab initio calculations of the pressure-induced structural phasetransitions for four II-VI compounds

Research paper thumbnail of Phonon Softening and Superconductivity in Tellurium under Pressure

Physical Review Letters, 1996

The phonon dispersion and the electron-phonon interaction for the beta\betabeta-Po and the bcc high pre... more The phonon dispersion and the electron-phonon interaction for the beta\betabeta-Po and the bcc high pressure phases of tellurium are computed with density-functional perturbation theory. Our calculations reproduce and explain the experimentally observed pressure dependence of the superconducting critical temperature (T$_{\rm c}$) and confirm the connection between the jump in T$_{\rm c}$ and the structural phase transition. The phonon contribution to the free energy is shown to be responsible for the difference in the structural transition pressure observed in low and room temperature experiments.

Research paper thumbnail of Band structure of CdS and CdSe at high pressure

Research paper thumbnail of Dynamical screening at the metal - semiconductor interface and excitonic superconductivity

Journal of Physics-condensed Matter, 1997

We examine the possibility of excitonic superconductivity at a metal - semiconductor interface. A... more We examine the possibility of excitonic superconductivity at a metal - semiconductor interface. An ab initio RPA calculation of the screened Coulomb electron - electron interaction is performed for the silicon - jellium multilayer model. The superconducting kernel for this multilayered system is found to be positive in the whole frequency range considered. We show that the inclusion of local field effects does not change the sign of the kernel and thus does not enhance the excitonic mechanism.

Research paper thumbnail of Phonon softening and superconductivity in tellurium under pressure

The phonon dispersion and the electron-phonon interaction for the beta\betabeta-Po and the bcc high pre... more The phonon dispersion and the electron-phonon interaction for the beta\betabeta-Po and the bcc high pressure phases of tellurium are computed with density-functional perturbation theory. Our calculations reproduce and explain the experimentally observed pressure dependence of the superconducting critical temperature (T$_{\rm c}$) and confirm the connection between the jump in T$_{\rm c}$ and the structural phase transition. The phonon contribution to the free energy is shown to be responsible for the difference in the structural transition pressure observed in low and room temperature experiments.

Research paper thumbnail of bold {ital Ab initio}} calculations of the pressure-induced structural phase transitions for four II-VI compounds