sentences:  In series of his works the development of methods of quantum statistical mechanics was considered in light of their applications to quantum solid-state theory.He discussed fundamental problems of the physics of magnetic materials and the methods of the quantum theory of magnetism, including the method of two-time temperature Green's functions which is widely used in various physical problems of many-particle systems
  with interaction.Quantum cooperative effects and quasi-particle dynamics in the basic microscopic models of quantum theory of magnetism