| This thesis is the result of the work that I have performed as a Ph.D student at the University of North Carolina at Chapel Hill. I have explored some consequences of the linearity of the energy dispersion and the effective lack of screening of the Coulomb interaction in a single sheet of graphite. As a consequence of the long-ranged interband interaction, the system is prone to the formation of an excitonic state associated with the opening of a singlet gap in the spectrum. The opening of this gap signals a metal to excitonic insulator transition which, unlike in the screened case studied by previous authors, only occurs if the Coulomb coupling is larger than a certain critical value. Finally, allowing triplet as well as singlet excitonic pairing, ferromagnetism arises naturally in our model in agreement with the behavior observed in samples of highly oriented pyrolytic graphite. |
