Antsygina T. Thermodynamic, kinetic, and magnetic properties of quantum solids at low temperatures

Objects - quantum solids: 3He-4He mixtures, p-H2 with impurities, N2-type cryocrystals, solutions of diatomic molecules in rare gase matrices, and quantum Heisenberg magnets. Goals: the development of rigorous theory of thermodynamic and kinetic phenomena in quantum solids and theoretical interpretation of experimentally observed effects. Methods: analytical methods of theoretical and mathematical physics such as Green function formalism, path integration, renormalization group technique, etc. New results: the thermodynamic theory for libron subsystem of N2-type cryocrystals in alpha-phase as well as solid solutions of diatomic impurities in Ar and Kr matrices is developed. An inelastic phonon scattering by pair orthoclusters in p-H2 is first shown to have the temperature threshold. The theory of the thermal conductivity in p-H2 with heavy impurities is developed, which explains complicated concentration and temperature dependences of the thermal conductivity as resulting from the interference of n ormal phonon-phonon processes, umklapp processes and resonance scattering at the heavy impurity. The theory of thermodynamic and kinetic properties of separating solid mixtures of helium isotopes is developed. For the first time it is obtained an adequate description for the temperature dependences of the heat capacity of 3He-4He solutions above the phase separation temperature. A number of approximate methods are constructed to describe analytically the thermodynamics of quantum Heisenberg magnets in a wide temperature range. The 3He monolayer solid on graphit in ferromagnetic regime is first proved to be a quantum Heisenberg magnet with S=1/2 on a triangular lattice. The effect of doping on both the Neel temparature and the temperature of superconducting transition for metal-oxide compounds are obtained. Introduction: All main results are used to interpret real experimental data and the theory agrees well with the experiment. Employment: the results are important for further investigations in physics of q uantum solids and low temperature physics.