December, 12 (2007) at 4pm

Rok Zitko
University of Ljubljana

Quantum impurity models play an important role in many fields of research in physics. For example, they describe quantum systems in interaction with environment (decoherence), magnetic impurities in bulk and on surfaces of metals (Kondo effect) and electrons trapped in nanostructures (transport phenomena). They also play a role of effective models in the dynamical mean field theory (DMFT) and they are used as toy models for testing new non-perturbative techniques in quantum field theory. In the seminar, I will introduce the concept of quantum impurities and describe the numerical renormalization group technique. For the purpose of studying thermodynamic and transport properties of multiple quantum dot structures, a new highly flexible implementation of the NRG has been developed. In particular, it allows easy setup of complex impurity cluster models and physical quantities to be computed: both can be described in terms of familiar and natural second quantization expressions. As an application, clusters of parallel quantum dots were recently explored, uncovering interesting quantum phase transitions.