Thermal Fluctuations and Electromagnetic Noise Spectra in Quantum Statistical Mechanics.

We derive the thermal noise spectrum of the of the longitudinal and transverse electric field operator of a given wave vector starting from the quantum-statistical definitions and relate it to the complex frequency and wave vector dependent complex conductivity in a homogeneous, isotropic system of electromagnetic interacting electrons. No additional assumptions were used in the proof. We analyze separately the longitudinal and transverse case with their peculiarities. The Nyquist formula for vanishing frequency and wave vector, as well as its modification for non-vanishing frequencies and wave vectors follow immediately. Furthermore we discuss also the noise of the photon occupation numbers.

К вопросу о влиянии неоднородного диэлектрического покрытия на характеристики металлической поверхности

Within the framework of the quantum-statistical functional and the Ritz method, the the problem of finding the surface energy per unit area and work function electrons of a metal flat surface with a inhomogeneous dielectric coating, taken into account in the approximation of a continuous medium. For a uniform coating, the calculated values are insensitive to the selection one-parameter functions for an electronic profile, but sensitive to the gradient series of kinetic energy non-interacting electrons. Calculations are performed for Al, Na and the comparison with the calculations by the Kohn-Shem method is made. Analytically the connection between the theory of the Ritz method for inhomogeneous coatings and calculations by the Kohn-Shem method work function of electrons for metal-dielectric nanosandwiches. As it turned out, the influence inhomogeneous coating on the characteristics of the metal surface can be scaled down to a uniform coverage case. The possibility of using the obtained results in various experimental situations are discussed.

On Strongly Correlated Eelectrons in Metals

A procedure, dedicated to superconductivity, is extended to study the properties of interacting electrons in normal metals in the thermodynamic limit. Each independent-electron band is shown to split into two correlated-electron bands. Excellent agreement is achieved with Bethe's wave-function for the one-dimensional Hubbard model. The groundstate energy, reckoned for the two-dimensional Hubbard Hamiltonian, is found to be lower than values, obtained thanks to the numerical methods. This analysis applies for any spatial dimension and temperature.

Optical Conductivity of Colossal Magnetoresistance Manganites

<p>The colossal magnetoresistance manganites are a group of materials whose unusual physical properties are a symptom of strongly interacting electrons and phonons. In order to elucidate some of these electronic and vibrational properties, an infrared optical investigation of manganites with a broad range of physical characteristics has been performed. Temperature-dependent normal incidence reflectivity measurements have been made on two samples of manganites, in the energy range of 60 cm-1 - 50000 cm-1, 1 for La0.9 Ca0.1 MnO3, an insulating ferromagnet, and 2 La0.735 Ca0.265 MnO3, a metallic ferromagnet. Temperature-dependent ellipsometric reflection measurements were performed in the energy range of 50 cm-1 - 5000 cm-1, on four faces of two samples of structurally anisotropic manganite, probing the 3. ab plane and c-axis of La1.2 Sr1.8 Mn2O7, a metallic ferromagnet, and 4. the ab plane and c-axis of PrSr2 Mn2O7, an insulating antiferromagnet. The optical conductivity for each of the first two samples has been deduced by a careful Kramers-Kronig analyis of the normal incidence reflectivity. For samples 3. and 4. the optical conductivity has been deduced by inversion of the ellipsometric constants, and a careful subsequent fitting to account for their anisotropy. The transition temperatures and types of magnetic order for all samples have also been characterised by magnetisation measurements. Treatment of the surface is shown to be critical in reflectivity measurements by the observation of hugely contrasting spectra, measured from a polished sample of metallic-like La0.735 Ca0.256 MnO3, before and after annealing. Several features observed in the measurements, especially for the layered materials, are consistent with the idea that a polaron, or electron-lattice interaction, is hugely important in a description of the electron dynamics of these materials. The correlation between spectral features and the structural and magnetic properties of the materials is investigated, finding that the cause of charge transport modification seen in the metallic-like materials could be explained by either a polaron or localisation due to disorder.</p>

Optical Conductivity of Colossal Magnetoresistance Manganites

<p>The colossal magnetoresistance manganites are a group of materials whose unusual physical properties are a symptom of strongly interacting electrons and phonons. In order to elucidate some of these electronic and vibrational properties, an infrared optical investigation of manganites with a broad range of physical characteristics has been performed. Temperature-dependent normal incidence reflectivity measurements have been made on two samples of manganites, in the energy range of 60 cm-1 - 50000 cm-1, 1 for La0.9 Ca0.1 MnO3, an insulating ferromagnet, and 2 La0.735 Ca0.265 MnO3, a metallic ferromagnet. Temperature-dependent ellipsometric reflection measurements were performed in the energy range of 50 cm-1 - 5000 cm-1, on four faces of two samples of structurally anisotropic manganite, probing the 3. ab plane and c-axis of La1.2 Sr1.8 Mn2O7, a metallic ferromagnet, and 4. the ab plane and c-axis of PrSr2 Mn2O7, an insulating antiferromagnet. The optical conductivity for each of the first two samples has been deduced by a careful Kramers-Kronig analyis of the normal incidence reflectivity. For samples 3. and 4. the optical conductivity has been deduced by inversion of the ellipsometric constants, and a careful subsequent fitting to account for their anisotropy. The transition temperatures and types of magnetic order for all samples have also been characterised by magnetisation measurements. Treatment of the surface is shown to be critical in reflectivity measurements by the observation of hugely contrasting spectra, measured from a polished sample of metallic-like La0.735 Ca0.256 MnO3, before and after annealing. Several features observed in the measurements, especially for the layered materials, are consistent with the idea that a polaron, or electron-lattice interaction, is hugely important in a description of the electron dynamics of these materials. The correlation between spectral features and the structural and magnetic properties of the materials is investigated, finding that the cause of charge transport modification seen in the metallic-like materials could be explained by either a polaron or localisation due to disorder.</p>

Thermal Fluctuations and Electromagnetic Noise Spectra in Quantum Statistical Mechanics

We derive the thermal noise spectrum of the Fourier transform of the electric field operator of a given wave vector starting from the quantum-statistical definitions and relate it to the complex frequency and wave vector dependent complex conductivity in a homogeneous, isotropic system of electromagnetic interacting electrons. We analyze separately the longitudinal and transverse case with their peculiarities. The Nyquist formula for vanishing frequency and wave vector, as well as its modification for non-vanishing frequencies and wave vectors follow immediately. Furthermore we discuss also the noise of the photon occupation numbers. It is important to stress that no additional assumptions at all were used in this straightforward proof.