Electron-Hole Symmetry and Magnetic Coupling in Antiferromagnetic LaFeAsO

Abstract

When either electron or hole doped at concentrations $x\sim 0.1$, the LaFeAsO family displays remarkably high temperature superconductivity with $T_c$ up to 55 K. In the most energetically stable ${\overrightarrow{Q}}_M=(\pi ,\pi ,0)$ antiferromagnetic (AFM) phase comprised of tetragonal-symmetry breaking alternating chains of aligned spins, there is a deep pseudogap in the Fe $3d$ states centered at the Fermi energy arising from light carriers ($m^{*}\sim 0.25–0.33$), and very strong magnetophonon coupling is uncovered. Doping (of either sign) beyond $x\sim 0.08$ results in heavy carriers per Fe (by roughly an order of magnitude) with a large Fermi surface. Calculated Fe-Fe transverse exchange couplings $J_{ij}(R)$ reveal that exchange coupling is strongly dependent on both the AFM symmetry and on the Fe-As distance.