Sharif Digital Repository

In this thesis, we consider the Kondo-necklace model to investigate the quantum phase transition between the Kondo-singlet and antiferromagnetic phases. There is no exact solution for this model. We would like to study the quantum critical behaviour of this model on one, two and three dimensional spaces in addition to ladder geometry. In this respect, we looked for a proper method which can give us some information for our model on any spaces mentioned above. Therefore, we implemented the perturbation continuous unitary transformation (PCUT) for the Kondo-necklace model. By using this method, we can not only calculate the ground state energy for 1, 2, 3 dimension and n-leg ladder... 

The fascinating subject of heavy fermion physics in rare-earth and actinide systems has been a challenge for theoretical and experimental investigations for decades. Kondo Necklace model is one of the promising models in the study of strongly-correlated heavy fermion compounds, which is studied in this project.One of the methods to diagonalize a Hamiltonian properly, regardless of system size, is the continuous unitary transformation. In this approach, the Hamiltonian is considered as a function of a flow parameter. The Hamiltonian is transformed to a simpler form (diagonal or band-block diagonal) under a flow equation which is based on applying infinite numbers of infinitesimal unitary...