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| BaFe2As2 | |
|---|---|
| Name | BaFe2As2 |
| Formula | BaFe2As2 |
| Crystal system | Tetragonal (room temperature) |
| Space group | I4/mmm |
BaFe2As2 is an iron-based pnictide compound notable for its layered tetragonal lattice and as a parent phase for high-temperature superconductivity. It is studied across condensed matter physics, materials science, and solid-state chemistry for its interplay of structural transitions, antiferromagnetism, and emergent superconductivity under chemical substitution or pressure. Investigations involve wide collaborations among institutions, national laboratories, universities, and instrument facilities.
The room-temperature structure adopts the ThCr2Si2-type motif common to 122 pnictides, with barium ions sandwiched between FeAs layers, closely related to structures examined in Elemental barium research, ThCr2Si2 structure surveys, and comparisons to LaFeAsO families. Lattice parameters are characterized by tetragonal symmetry in space group I4/mmm, and a temperature-driven tetragonal-to-orthorhombic transition parallels studies performed at Oak Ridge National Laboratory, Lawrence Berkeley National Laboratory, and university crystallography groups. The Fe atoms form a square planar net coordinated by As tetrahedra, echoing motifs in CuO2 planes analyses and structural motifs reported by teams at Max Planck Institute for Chemical Physics of Solids and Argonne National Laboratory.
Synthesis approaches include solid-state reactions, flux growth, and Bridgman techniques developed in laboratories such as Tokyo Institute of Technology and University of Cambridge. Common precursors mirror reagent handling protocols used at National Institute of Standards and Technology and Stanford University facilities, with tin- or FeAs-flux methods refined by groups at Paul Scherrer Institute and University of Maryland. High-pressure synthesis leveraging devices from Geophysical Laboratory and ISIS Neutron and Muon Source has produced samples for studies at European Synchrotron Radiation Facility and Deutsches Elektronen-Synchrotron. Thin-film growth via molecular beam epitaxy and pulsed laser deposition has been pursued at MIT and University of Tokyo to enable transport and spectroscopic measurements.
Bulk properties have been characterized through heat capacity, resistivity, magnetization, and thermal expansion studies in collaborations involving Los Alamos National Laboratory, Duke University, and University of California, Berkeley. The stoichiometric compound shows metallic conductivity and a pronounced anomaly in specific heat and resistivity at the magnetostructural transition, mirroring measurements from teams at Columbia University and Yale University. Elastic and phonon responses have been investigated with inelastic neutron and x-ray scattering at ILL Grenoble and SLAC National Accelerator Laboratory. Anisotropic transport and magnetoresistance studies reference techniques used by researchers at Princeton University and University of Illinois Urbana-Champaign.
Angle-resolved photoemission spectroscopy (ARPES) experiments at Stanford Synchrotron Radiation Lightsource and Diamond Light Source map the multiband Fermi surface, complementing density functional results from groups at Harvard University and University of Oxford. The parent compound exhibits stripe-like antiferromagnetic order; neutron diffraction studies at Institute Laue-Langevin and muon spin rotation performed by teams at Paul Scherrer Institute detail ordered moment size and ordering vectors. Band-structure calculations reference frameworks developed at Los Alamos National Laboratory and functional benchmarks from IBM Research and University of California, Santa Barbara. Correlation effects and Hund's coupling discussions draw on theoretical developments at Rutgers University and University of Michigan.
Superconductivity is induced by chemical substitution (K, Co, Ni, P, Ru) or external pressure, a phenomenon explored in phase diagrams reported by researchers at University of Science and Technology of China, Queens University Belfast, and ETH Zurich. Hole-doping via potassium and electron-doping via cobalt were characterized using techniques pioneered at Tsinghua University and University of Twente, while isovalent substitutions and pressure studies were advanced at Max Planck Institute for Solid State Research and Argonne National Laboratory. The dome-shaped superconducting region and coexistence of magnetism and superconductivity echo findings in cuprate studies at University of Chicago and heavy-fermion comparisons from University of California, San Diego.
Key probes include x-ray diffraction at Advanced Photon Source, neutron scattering at Oak Ridge National Laboratory, ARPES at Stanford Synchrotron Radiation Lightsource, scanning tunneling microscopy at IBM Almaden Research Center, and muon spin rotation at Paul Scherrer Institute. Transport measurements, Hall effect, and NMR studies referenced methodologies from University of Colorado Boulder and ETH Zurich. Calorimetry, thermal expansion, and dilatometry applied techniques similar to those at National High Magnetic Field Laboratory and Los Alamos National Laboratory to extract entropy and coupling constants.
Theoretical descriptions employ multi-orbital Hubbard and itinerant spin-density-wave models developed by groups at Princeton University, Cornell University, and University of Cambridge. First-principles calculations using density functional theory and dynamical mean-field theory have been advanced at École Polytechnique Fédérale de Lausanne and Beijing Computational Science Research Center. Spin fluctuation and nematicity frameworks draw on work from Columbia University, Stanford University, and Max Planck Institute for the Physics of Complex Systems. Phenomenological Ginzburg–Landau treatments and renormalization-group analyses are included in theoretical syntheses authored by researchers at University of Illinois Urbana-Champaign and University of Tokyo.
Category:Iron-based superconductors Category:ThCr2Si2-type compounds