LaFeAsO

LaFeAsO
Name	LaFeAsO
Caption	Layered structure of LaFeAsO
Formula	LaFeAsO
Crystal system	Tetragonal (room temperature)
Space group	P4/nmm
Color	Metallic gray

LaFeAsO is an iron-based layered oxyarsenide that became central to condensed matter research after the discovery of high-temperature superconductivity in doped variants. Its structure and electronic behavior connect to research carried out at institutions such as University of Tokyo, Max Planck Society, University of Cambridge, Massachusetts Institute of Technology, and University of Tokyo collaborators, and it motivated experimental programs at facilities like CERN and National Institute of Standards and Technology. LaFeAsO links materials chemistry, solid-state physics, and computational studies performed by groups associated with Harvard University, Stanford University, and ETH Zurich.

Composition and Crystal Structure

LaFeAsO is composed of alternating layers of lanthanum-oxygen and iron-arsenic; the stacking produces a quasi-two-dimensional motif relevant to layered materials studied at Bell Labs and IBM Research. The unit cell belongs to the P4/nmm space group, analogous to other layered compounds examined by researchers at Max Planck Institute for Solid State Research and Argonne National Laboratory. The FeAs layers host tetrahedrally coordinated iron atoms, an arrangement comparable to structures investigated in Perovskite research and contrasted with cuprate frameworks studied at Princeton University. Lattice parameters and internal atomic positions were refined in crystallographic work involving teams from University of Tokyo, Kyoto University, and University of California, Berkeley and reported alongside techniques used at Diamond Light Source and APS (Advanced Photon Source).

Electronic and Magnetic Properties

The electronic structure of LaFeAsO features multiple Fermi surface sheets derived from Fe 3d orbitals, a complexity explored by theorists at MIT, University of Illinois Urbana-Champaign, and University of Oxford. Angle-resolved photoemission spectroscopy measurements performed at MAX IV Laboratory and Swiss Light Source resolved band dispersions that echo studies from Columbia University and University of Cambridge. Magnetically, the parent compound exhibits spin-density-wave order stemming from nesting of electron and hole pockets; neutron scattering experiments at Institut Laue–Langevin, ISIS Neutron and Muon Source, and Oak Ridge National Laboratory characterized stripe-like antiferromagnetism similar to phenomena reported in work by teams at Los Alamos National Laboratory and Brookhaven National Laboratory. The interplay of Hund’s coupling and itinerancy was discussed in theoretical contributions from École Normale Supérieure, Weizmann Institute of Science, and University of Tokyo.

Superconductivity and Phase Diagram

Superconductivity emerges in doped or pressurized LaFeAsO, a discovery that spurred efforts at University of Tokyo, Chinese Academy of Sciences, and Rice University. Substitutions such as fluorine for oxygen or oxygen deficiency shift the phase boundary between magnetism and superconductivity, motifs examined by researchers at University of Geneva, University of Maryland, and University of Houston. High-pressure experiments conducted at Lawrence Livermore National Laboratory and Institut de Physique du Globe de Paris mapped Tc evolution, while muon spin rotation studies at Paul Scherrer Institute and heat-capacity measurements at University of Bristol delineated superconducting gaps, invoking comparisons with pairing scenarios debated at Harvard University, University of Cambridge, and University of Tokyo.

Synthesis and Sample Preparation

Samples of LaFeAsO have been synthesized by solid-state reaction methods developed in laboratories at Tohoku University, University of Tokyo, and Peking University. High-pressure synthesis routes were refined at National High Magnetic Field Laboratory and Tokyo Institute of Technology to stabilize stoichiometry and enhance crystallinity. Techniques such as high-temperature annealing, flux growth, and pulsed laser deposition adapted from protocols at Riken, Oak Ridge National Laboratory, and Los Alamos National Laboratory produced polycrystalline pellets and thin films used in transport studies undertaken by groups at University of California, San Diego and University of Illinois Urbana-Champaign. Sample handling and safety followed practices aligned with standards from International Atomic Energy Agency and materials labs at National Institute for Materials Science.

Experimental Methods and Characterization

Characterization of LaFeAsO employed X-ray diffraction, neutron diffraction, and electron microscopy performed at facilities like European Synchrotron Radiation Facility, Brookhaven National Laboratory, and Argonne National Laboratory. Spectroscopies including ARPES, Raman, and infrared measurements were carried out at Stanford Synchrotron Radiation Lightsource, Elettra, and SLAC National Accelerator Laboratory. Transport and thermodynamic experiments — resistivity, Hall effect, specific heat, and magnetization — were conducted in labs affiliated with Columbia University, University of Tokyo, and University of Cambridge, while muon spin rotation and Mössbauer spectroscopy at Paul Scherrer Institute and TRIUMF probed local magnetism. Data analysis used electronic structure tools developed in collaborative projects involving Los Alamos National Laboratory, Oak Ridge National Laboratory, and Lawrence Berkeley National Laboratory.

Theoretical Models and Calculations

Theoretical descriptions of LaFeAsO used density functional theory, dynamical mean-field theory, and multiorbital Hubbard models, methodologies advanced at Princeton University, Max Planck Institute for Chemical Physics of Solids, and Rutgers University. First-principles bandstructure work from Cornell University, University of Vienna, and University of Michigan clarified orbital characters, while spin-fluctuation pairing theories were developed by groups at University of Cambridge, University of Tokyo, and University of Illinois Urbana-Champaign. Computational codes and frameworks employed included projects associated with Argonne National Laboratory, Oak Ridge National Laboratory, and Lawrence Berkeley National Laboratory, and conceptual parallels were drawn to theoretical studies from École Polytechnique, Imperial College London, and California Institute of Technology.

Category:Iron-based superconductors