Dynamical properties of single-electron devices and molecular magnets

摘要

This doctoral dissertation consists of theoretical studies of a number of nanometer-scale structures.In papers [1]-[5], the emphasis is on tiny devices based on conducting materials, i.e., metals and doped semiconductors. Depending on the feature size, geometry, and the electronic density of states, charging effects and quantization of single-electron states may occur. These properties can be utilized to control charge and electric current with the precision of fractions of the electronic charge e - hence the name single-electron device.In paper [6] the focus is on the rich magnetization dynamics of the molecular magnet Mn acetate. At low temperature the molecules of this material acquire a magnetic single-spin ground state with S=10. Interestingly, the quantum tunneling of the molecular spins between the different spin states is manifest even in the magnetization relaxation of macroscopic samples.In order to study or utilize the quantized states in a given nanostructure, this needs to be coupled to some measuring device. The coupling always gives rise to exchange of particles and/or heat between the nanostructure and its environment and the stronger the coupling the more the environment affects the smaller system. This may lead to modifications in the quantized states, interference effects, and dissipation. In some cases, even completely new many-body states such as the Kondo resonances observed in ultrasmall quantum dots are found to emerge. All these effects are of great fundamental as well as of nanoengineering interest.In this thesis, a theoretical model applicable to all the above systems is developed and used. The real-time diagrammatic technique is well suited for describing the various strong-coupling effects between a set of localized states and its fermionic and/or bosonic environment. This approach also allows the description of the nonequilibrium conditions attained in single-electron devices.