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All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Electronic and magnetic properties of the topological semimetal SmMg 2 Bi 2

Dirac semimetals show nontrivial physical properties and can host exotic quantum states like Weyl semimetals and topological insulators under suitable external conditions. Here, by combining angle-resolved photoemission spectroscopy measurements (ARPES) and first-principle calculations, we demonstrate that the Zintl-phase compound SmMg 2 Bi 2 is in close proximity to a topological Dirac semimetallic state. ARPES results show a Dirac-like band crossing at the zone center near the Fermi level (E F ), which is further confirmed by first-principle calculations. Theoretical studies also reveal that SmMg 2 Bi 2 belongs to a Z 2 topological class and hosts spin-polarized states around the E F . Zintl's theory predicts that the valence state of Sm in this material should be Sm 2+ , however, we detect many Sm-4f multiplet states (flat-bands) whose energy positions and relative intensities suggest the presence of both dominant Sm 2+ and minor Sm 3+ . The small concentration (2.5%) of Sm 3+ in the bulk of a crystal is inferred to arise from Sm vacancies in the crystal. It is also evident that these flat bands and other dispersive states are strongly hybridized when they cross each other. Due to the presence of Sm 3+ ions, the temperature dependence of the magnetic susceptibility χ (T) shows a Curie-Weiss-like contribution in the low-temperature region, in addition to the Van Vleck-like behavior expected for the Sm 2+ ions. The present study will help to better understand the electronic structure, magnetism, and transport properties of related materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Materials Data on SmMg by Materials Project

SmMg is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Mg is bonded in a body-centered cubic geometry to eight equivalent Sm atoms. All Mg–Sm bond lengths are 3.33 Å. Sm is bonded in a body-centered cubic geometry to eight equivalent Mg atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SmMg(BO2)5 by Materials Project

MgSm(BO2)5 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Mg2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Mg–O bond distances ranging from 2.08–2.37 Å. Sm3+ is bonded in a 10-coordinate geometry to ten O2- atoms. There are a spread of Sm–O bond distances ranging from 2.32–2.97 Å. There are five inequivalent B3+ sites. In the first B3+ site, B3+ is bonded to four O2- atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.47–1.50 Å. In the second B3+ site, B3+ is bonded to four O2- atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.47–1.50 Å. In the third B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. There is one shorter (1.37 Å) and two longer (1.38 Å) B–O bond length. In the fourth B3+ site, B3+ is bonded to four O2- atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.46–1.51 Å. In the fifth B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of B–O bond distances ranging from 1.36–1.40 Å. There are ten inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 120 degrees geometry to one Sm3+ and two B3+ atoms. In the second O2- site, O2- is bonded in a 2-coordinate geometry to one Mg2+, one Sm3+, and two B3+ atoms. In the third O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two equivalent Sm3+ and two B3+ atoms. In the fourth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Mg2+, one Sm3+, and two B3+ atoms. In the fifth O2- site, O2- is bonded in a 1-coordinate geometry to two equivalent Mg2+, one Sm3+, and one B3+ atom. In the sixth O2- site, O2- is bonded in a distorted single-bond geometry to two equivalent Sm3+ and one B3+ atom. In the seventh O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Sm3+ and two B3+ atoms. In the eighth O2- site, O2- is bonded in a 3-coordinate geometry to one Mg2+ and two B3+ atoms. In the ninth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mg2+ and two B3+ atoms. In the tenth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Sm3+ and two B3+ atoms.

36 MATERIALS SCIENCE↗