Tuesday 24.06.2008 - 14h15-15h15, SE7


Quantum phase transitions in the Ising-Falicov-Kimball model

Julia Wildeboer, Univ. Dresden

The main aim of the diploma thesis is to discover the phase diagram of the so-called Ising-Falicov-Kimball modell (Ising-FKM) using the recently introduced new method of renormalisation, the projector-based renormalisation method (PRM). This modell, containing two types of electrons, localized f-electrons and conduction electrons, interacting via a density-density-term (U) and a new spin-dependend term of Ising type (J), was recently proposed by Lemanski in order to describe materials which show a charge ordered structure accompanied by a spin ordered structure. Several different states which are either purely charge ordered or purely spin ordered are found. Additionally,quantum phase transitions from a charge ordered phase into a spin ordered one dependend on the ratio of the coupling parameters $U/J$ are shown. A special feature of the antiferromagnetic state and the corresponding charge ordered state is the appearance of the gap in the single-particle energies of the conduction electrons at the Fermi vektor k_F when half-filling is considered. Finally, we show the abrupt destruction of the order by thermal fluctuations due to increasing temperature.