Orbital Aspect of Iron-based Superconductivity – Wei-Cheng Lee

Date: Mon. November 4th, 2013, 12:30 pm-1:30 pm
Location: Rockefeller 221

In this talk, I will focus on the new classes of high-temperature superconductors, iron pnictides. While the magnetic interactions are certainly important in these materials, there have been significant evidences suggesting that the orbital degrees of freedom could play an important role as well. From both theoretical and experimental aspects, I will argue that the orbital degrees of freedom do play a game-changing role in physical properties of iron based superconductors. I will show that at the single particle level, the orbital order in the quasi-1D dxz and dyz bands induces a distortion of the Fermi surface, which could result in the structural phase transition. Furthermore, fluctuations associated with the orbital order could drive a non-Fermi liquid behavior in the critical region near the orbital ordering phase transition. Even for the magnetic properties, I will show that orbital order and fluctuations can qualitatively change the nature of the magnetic excitation spectrum. Several experiments supporting these theoretical ideas will be discussed.