• Can Anti-Ferromagnetism And Anisotropic Superconductivity Coexist In Iron Pnictides?

      Newman, Joseph; Department of Chemistry and Physics (2016-03)
      By treating both anti-ferromagnetism (AFM) and superconductivity (SC) on an equal footing, we investigate the possible coexistence of AFM and SC of recently found high-temperature superconducting compounds. Assuming that the electron pairing is mediated by the spin fluctuations and using a mean-field theory, we derive a set of gap equations for both AFM and SC order parameters. In the spirit of the second order phase transition, we then linearize the gap equations using various base functions for superconducting order to include the different pairing symmetries. By analyzing the solution of our linearized equations, we then discuss the possible coexistence of AFM and anisotropic SC in these compounds.
    • Studying the Interplay between Superconductivity and Anti-Ferromag-Netism through Bose-Fermi Mixtures on Optical Lattices

      Brackett, Jeremy; Department of Chemistry and Physics (2016-03)
      Motivated by the recent experimental progress with ultra-cold atoms, we investigate the physics of a Bose-Fermi mixture on a two dimensional optical lattice. We treat the system parameters such that 2-component fermions are in a deep external trap and weakly interacting bosons are in a shallow external trap, however both of these atoms are subjected to the same optical lattice. In this parameter regime, the bosons form a Bose-Einstein condensate and mediate an attractive interaction between fermions through low energy Bose excitations. As a result, the dynamics of the fermions can be described by the single band Hubbard model that involves on-site repulsive interaction and elementary excitation mediated attractive interactions. Using a mean field theory, we derive an effective action up to the quartic order in both d-wave superconducting and anti-ferromagnetic order parameters. Using this Landau energy functional, we then discuss the phase transition and study the competition and/or cooperation of anti-ferromagnetism and d-wave superconductivity in the system.