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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Sr3Ir2O7 by Materials Project

Sr3Ir2O7 crystallizes in the orthorhombic Ccce space group. The structure is three-dimensional. there are two inequivalent Sr2+ sites. In the first Sr2+ site, Sr2+ is bonded in a 12-coordinate geometry to eight O2- atoms. There are four shorter (2.53 Å) and four longer (2.79 Å) Sr–O bond lengths. In the second Sr2+ site, Sr2+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Sr–O bond distances ranging from 2.43–2.79 Å. Ir4+ is bonded to six O2- atoms to form corner-sharing IrO6 octahedra. The corner-sharing octahedra tilt angles range from 0–28°. There are a spread of Ir–O bond distances ranging from 2.03–2.06 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded to five equivalent Sr2+ and one Ir4+ atom to form a mixture of distorted edge and corner-sharing OSr5Ir octahedra. The corner-sharing octahedra tilt angles range from 0–6°. In the second O2- site, O2- is bonded in a 4-coordinate geometry to two Sr2+ and two equivalent Ir4+ atoms. In the third O2- site, O2- is bonded to four equivalent Sr2+ and two equivalent Ir4+ atoms to form distorted OSr4Ir2 octahedra that share corners with six OSr5Ir octahedra and edges with four equivalent OSr4Ir2 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr3Ir2O7 by Materials Project

Sr3Ir2O7 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent Sr2+ sites. In the first Sr2+ site, Sr2+ is bonded to twelve O2- atoms to form SrO12 cuboctahedra that share corners with four equivalent SrO12 cuboctahedra, faces with four equivalent SrO12 cuboctahedra, and faces with eight equivalent IrO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.64–3.07 Å. In the second Sr2+ site, Sr2+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of Sr–O bond distances ranging from 2.47–2.91 Å. Ir4+ is bonded to six O2- atoms to form IrO6 octahedra that share corners with five equivalent IrO6 octahedra and faces with four equivalent SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–16°. There are a spread of Ir–O bond distances ranging from 2.00–2.04 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded to five equivalent Sr2+ and one Ir4+ atom to form a mixture of distorted corner and edge-sharing OSr5Ir octahedra. The corner-sharing octahedra tilt angles range from 1–10°. In the second O2- site, O2- is bonded to four equivalent Sr2+ and two equivalent Ir4+ atoms to form distorted OSr4Ir2 octahedra that share corners with six OSr5Ir octahedra and edges with four equivalent OSr4Ir2 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. In the third O2- site, O2- is bonded in a 6-coordinate geometry to four Sr2+ and two equivalent Ir4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Antiferromagnetic excitonic insulator state in Sr3Ir2O7

Abstract Excitonic insulators are usually considered to form via the condensation of a soft charge mode of bound electron-hole pairs. This, however, presumes that the soft exciton is of spin-singlet character. Early theoretical considerations have also predicted a very distinct scenario, in which the condensation of magnetic excitons results in an antiferromagnetic excitonic insulator state. Here we report resonant inelastic x-ray scattering (RIXS) measurements of Sr 3 Ir 2 O 7 . By isolating the longitudinal component of the spectra, we identify a magnetic mode that is well-defined at the magnetic and structural Brillouin zone centers, but which merges with the electronic continuum in between these high symmetry points and which decays upon heating concurrent with a decrease in the material’s resistivity. We show that a bilayer Hubbard model, in which electron-hole pairs are bound by exchange interactions, consistently explains all the electronic and magnetic properties of Sr 3 Ir 2 O 7 indicating that this material is a realization of the long-predicted antiferromagnetic excitonic insulator phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗