Pseudospin pairing and transport in atomic Fermi gases and bilayer systems

In this Thesis we consider the behavior of the drag conductivity close to exciton condensation in bilayer systems and close to the superfluid transition in cold Fermi gases. In chapter 2 we calculate the transition temperature for exciton condensation in double-layer graphene, showing that the remote bands can play a supporting role in this transition. In chapter 3 we consider a topological insulator thin film and calculate the behavior of the drag resistivity close to the transition temperature. We find a strong enhancement which can be used as a precursor for the transition. In chapter 4 we discuss an ultracold Fermi gas close to the superconducting transition and compare two different methods to obtain the drag resistivity, each taking into account a different phenomenon which affects the drag resistivity close to the transition. Finally, in chapter 5, we present a uniform theoretical framework to determine the drag resistivity in all experimental systems considered in this Thesis.