The Delicate Electronic and Magnetic Structure of the LaOFePn System (Pn = pnictogen)

Abstract

The occurrence of high temperature superconductivity, and the competition with magnetism, in stoichiometric and doped LaOFeAs and isostructural iron-oxypnictides is raising many fundamental questions about the electronic structure and magnetic interactions in this class of materials. There are now sufficient experimental data that it may be possible to identify the important issues whose resolution will lead to the understanding of this system. In this paper we address a number of the important issues. One important characteristic is the Fe-As distance (or more abstractly the pnictogen (Pn) height $z$(Pn)); we present results for the effect of $z$(Pn) on the electronic structure, energetics, and Fe magnetic moment. We also study LaOFeAs under pressure, and investigate the effects of both electron and hole doping within the virtual crystal approximation. The electric field gradients for all atoms in the LaOFeAs compound are presented (undoped and doped) and compared with available data. The observed $(\pi ,\pi ,\pi )$ magnetic order is studied and compared with the computationally simpler $(\pi ,\pi ,0)$ order which is probably a very good model in most respects. We investigate the crucial role of the pnictogen atom in this class, and predict the structures and properties of the N and Sb counterparts that have not yet been reported experimentally. At a certain volume a gap opens at the Fermi level in LaOFeN, separating bonding from antibonding bands and suggesting directions for a better simple understanding of the seemingly intricate electronic structure of this system. Finally, we address briefly on the possible effects of post-lanthanum rare earths, which have been observed to enhance the superconducting critical temperature substantially.

submitted to New Journal of Physics, special issue of iron-based superconductors

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• Possible three dimensional nodes in the $s\pm$ superconducting gap of BaFe${}_2$(As${}_{1-x}$P${}_x$)${}_2$
• Th substituted SmFeAsO: structural details and superconductivity with Tc above 50 K
• Tight binding model for iron pnictides
• Electronic properties of LaOFFeAs in the normal state probed by NMR/NQR
• Crystal Symmetry and Magnetic Order in Iron Pnictides: a Tight Binding Wannier Function Analysis
• Antiphase magnetic boundaries in iron-based superconductors: A first-principle density-functional theory study
• Emergence of superconductivity in single-crystalline LaFeAsO under simultaneous Sm and P substitution
• Magnetism driven by strong electronic correlation in the heavily carrier-doped iron oxypnictide LaFeAsO${}_{0.49}$H${}_{0.51}$