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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on BaFe2Se3 by Materials Project

BaFe2Se3 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ba2+ is bonded in a 9-coordinate geometry to nine Se2- atoms. There are a spread of Ba–Se bond distances ranging from 3.38–3.78 Å. Fe2+ is bonded to four Se2- atoms to form a mixture of edge and corner-sharing FeSe4 tetrahedra. There are a spread of Fe–Se bond distances ranging from 2.43–2.47 Å. There are three inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 5-coordinate geometry to three equivalent Ba2+ and two equivalent Fe2+ atoms. In the second Se2- site, Se2- is bonded in a 6-coordinate geometry to two equivalent Ba2+ and four equivalent Fe2+ atoms. In the third Se2- site, Se2- is bonded in a 6-coordinate geometry to four equivalent Ba2+ and two equivalent Fe2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BaFe2Se3 by Materials Project

BaFe2Se3 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. Ba2+ is bonded in a 8-coordinate geometry to eight Se2- atoms. There are a spread of Ba–Se bond distances ranging from 3.43–3.54 Å. Fe2+ is bonded to four Se2- atoms to form a mixture of edge and corner-sharing FeSe4 tetrahedra. There are two shorter (2.42 Å) and two longer (2.46 Å) Fe–Se bond lengths. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 6-coordinate geometry to two equivalent Ba2+ and four equivalent Fe2+ atoms. In the second Se2- site, Se2- is bonded in a 5-coordinate geometry to three equivalent Ba2+ and two equivalent Fe2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Block orbital-selective Mott insulators: A spin excitation analysis

We present a comprehensive study of the spin excitations—as measured by the dynamical spin structure factor S(q,ω)—of the so-called block-magnetic state of low-dimensional orbital-selective Mott insulators. We realize this state via both a multi-orbital Hubbard model and a generalized Kondo-Heisenberg Hamiltonian. Due to various competing energy scales present in the models, the system develops periodic ferromagnetic islands of various shapes and sizes, which are antiferromagnetically coupled. The 2×2 particular case was already found experimentally in the ladder material BaFe2Se3 that becomes superconducting under pressure. Here we discuss the electronic density as well as Hubbard and Hund coupling dependence of S(q,ω) using density matrix renormalization group method. Several interesting features were identified: (1) An acoustic (dispersive spin-wave) mode develops. (2) The spin-wave bandwidth establishes a new energy scale that is strongly dependent on the size of the magnetic island and becomes abnormally small for large clusters. (3) Optical (dispersionless spin excitation) modes are present for all block states studied here. In addition, a variety of phenomenological spin Hamiltonians have been investigated but none matches entirely our results that were obtained primarily at intermediate Hubbard U strengths. Our comprehensive analysis provides theoretical guidance and motivation to crystal growers to search for appropriate candidate materials to realize the block states, and to neutron scattering experimentalists to confirm the exotic dynamical magnetic properties unveiled here, with a rich mixture of acoustic and optical features.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗