FeSe

FeSe
Name	Iron(II) selenide
Formula	FeSe
Molar mass	134.81 g·mol⁻¹
Appearance	metallic gray crystalline solid
Crystal system	tetragonal (room temp), orthorhombic (low temp)
Melting point	~1340 °C (decomposes)
Conductivity	superconducting below Tc

FeSe

FeSe is an iron chalcogenide compound notable for its superconducting, nematic, and magnetic behaviors observed in bulk crystals, thin films, and heterostructures. Discovered in the context of iron-based superconductivity alongside materials investigated by researchers at institutions like University of Tokyo, Max Planck Society, and Brookhaven National Laboratory, FeSe has become a benchmark for studies linking crystallography, electronic structure, and emergent quantum phases. Its simple stoichiometry has attracted experimental campaigns at facilities such as Stanford University, MIT, Lawrence Berkeley National Laboratory, and Cambridge University.

Overview

FeSe crystallizes in a layered structure related to the family discovered during the early work at University of Tokyo and later explored by groups at Chinese Academy of Sciences, RIKEN, and Paul Scherrer Institute. The material features square planar layers of transition metal sites that connect to broad investigations at Argonne National Laboratory, Oak Ridge National Laboratory, and SLAC National Accelerator Laboratory into pairing mechanisms relevant to Nobel Prize-level themes in condensed matter. FeSe has been a subject in conferences organized by American Physical Society, European Physical Society, and Materials Research Society.

Crystal Structure and Synthesis

FeSe adopts the PbO-type tetragonal structure at ambient conditions, with a structural transition to an orthorhombic arrangement on cooling; these transformations were characterized using diffraction performed at Brookhaven National Laboratory, European Synchrotron Radiation Facility, and Diamond Light Source. Synthesis routes include chemical vapor transport developed with catalysts in collaboration between groups at University of Science and Technology of China and Tohoku University, flux methods pioneered by teams at University of Tokyo and University of Cambridge, and molecular beam epitaxy optimized by researchers at University of California, Berkeley and National Institute for Materials Science. High-pressure synthesis and tuning performed at Argonne National Laboratory and Institute for High Pressure Physics reveal polymorphs related to phases studied at Max Planck Institute for Solid State Research.

Electronic Structure and Superconductivity

Angle-resolved photoemission spectroscopy experiments conducted at beamlines operated by SLAC National Accelerator Laboratory, Paul Scherrer Institute, and ELETTRA mapped the multi-band Fermi surface, showing electron and hole pockets tied to orbitals discussed in theoretical work from Princeton University, Harvard University, and University of Illinois Urbana-Champaign. Density functional theory calculations performed by groups at Oak Ridge National Laboratory and University of Cambridge and many-body studies from Institute for Advanced Study and Perimeter Institute address correlations and pairing channels. Bulk Tc near 8–9 K contrasts with dramatically enhanced Tc reported in monolayer films on substrates such as SrTiO3, with landmark experiments at University of Tokyo and Tsinghua University reporting signatures consistent with unconventional pairing mechanisms explored in reviews by Nature Physics and Physical Review Letters authors.

Nematicity and Magnetism

The nematic phase of FeSe, characterized by rotational symmetry breaking without long-range stripe order, has been central to investigations by teams at Stanford University, University of Tokyo, and University of Maryland. Elastic shear modulus studies at Helmholtz-Zentrum Berlin and Raman scattering at Institut Laue-Langevin revealed coupling between lattice and electronic degrees of freedom discussed in theoretical frameworks by researchers at Columbia University and Yale University. Magnetic fluctuations probed by inelastic neutron scattering at facilities including Oak Ridge National Laboratory and Institut Laue-Langevin highlight contrasts with stripe-ordered iron pnictides studied at Max Planck Institute for Chemical Physics of Solids.

Physical Properties and Phase Diagram

Temperature-, pressure-, and doping-dependent phase diagrams were mapped in experiments led by groups at University of Science and Technology of China, University of Tokyo, and Riken Center for Emergent Matter Science, showing competing nematic, magnetic, and superconducting pockets akin to phase competition described in studies at Columbia University and University of Cambridge. Transport measurements performed at MIT and Harvard University display anisotropic resistivity and Hall coefficient behavior, while thermodynamic probes at University of Tokyo and ETH Zurich provide specific heat signatures used to infer gap structure. High-pressure experiments at Geophysical Laboratory and Los Alamos National Laboratory tune Tc and reveal collapsed tetragonal tendencies paralleling observations in other iron-based systems examined at Max Planck Society.

Thin Films, Interfaces, and Heterostructures

Monolayer FeSe grown by molecular beam epitaxy on SrTiO3 substrates was pioneered by collaborations involving University of Tokyo, Tsinghua University, and Stanford University, producing superconducting gaps and replica band features probed by ARPES at SLAC National Accelerator Laboratory and scanning tunneling microscopy at Lawrence Berkeley National Laboratory. Heterostructures combining FeSe with oxides such as BaTiO3 and interfaces engineered at IBM Research or Hitachi have been explored for interfacial electron-phonon coupling and charge transfer effects, with complementary transport and spectroscopic studies at Max Planck Institute and University of California, Los Angeles.

Applications and Experimental Techniques

While practical applications remain exploratory, potential uses in superconducting electronics, sensors, and platforms for studying topological superconductivity have been proposed by researchers at MIT, Caltech, and University of California, Berkeley. Key experimental techniques applied across laboratories including Brookhaven National Laboratory, Argonne National Laboratory, and Diamond Light Source encompass angle-resolved photoemission spectroscopy, inelastic neutron scattering, scanning tunneling microscopy, transport under extreme conditions at Los Alamos National Laboratory, and muon spin rotation at Paul Scherrer Institute. Ongoing collaborations between institutions such as Japanese Society for the Promotion of Science, National Science Foundation, and European Research Council support multidisciplinary efforts to elucidate pairing symmetry, phase competition, and device integration.

Category:Iron compounds Category:Superconductors