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Bulk and surface electronic structure of NiBi 3

Here, we present a high-resolution, angle-resolved photoemission spectroscopy study of the normal electronic state of the superconducting NiBi 3 . Our experimental results show a complex Fermi surface structure with many sheets along the Γ–$\textit{X}$ and Γ–$\textit{Y}$ directions of the Brillouin zone. The band structure presents a topological surface state (TSS) at the high symmetry Γ point with a surface Dirac point at the energy –0.185 eV. The Dirac-like cone presents a linear dispersion along $k_x$ while it presents saddle-like states along $k_y$ located in the vicinity of the surface Dirac point. Our results are in good agreement with results of density functional theory band structure calculations. We also discuss the topological band structure of the NiBi 3 compound.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Materials Data on NiBi by Materials Project

NiBi is Tungsten Carbide-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ni is bonded to six equivalent Bi atoms to form a mixture of distorted corner and edge-sharing NiBi6 pentagonal pyramids. All Ni–Bi bond lengths are 2.75 Å. Bi is bonded to six equivalent Ni atoms to form a mixture of corner, edge, and face-sharing BiNi6 octahedra. The corner-sharing octahedral tilt angles are 44°.

36 MATERIALS SCIENCE↗

Materials Data on Nd(NiBi)2 by Materials Project

Nd(NiBi)2 crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. Nd is bonded in a 12-coordinate geometry to eight Ni and nine Bi atoms. There are four shorter (3.34 Å) and four longer (3.62 Å) Nd–Ni bond lengths. There are a spread of Nd–Bi bond distances ranging from 3.49–3.65 Å. There are two inequivalent Ni sites. In the first Ni site, Ni is bonded in a 9-coordinate geometry to four equivalent Nd and five Bi atoms. There are one shorter (2.57 Å) and four longer (2.66 Å) Ni–Bi bond lengths. In the second Ni site, Ni is bonded in a 8-coordinate geometry to four equivalent Nd and four equivalent Bi atoms. All Ni–Bi bond lengths are 2.66 Å. There are two inequivalent Bi sites. In the first Bi site, Bi is bonded in a 5-coordinate geometry to five equivalent Nd and five Ni atoms. In the second Bi site, Bi is bonded in a 4-coordinate geometry to four equivalent Nd and four equivalent Ni atoms.

36 MATERIALS SCIENCE↗

Materials Data on Sm(NiBi)2 by Materials Project

Sm(NiBi)2 crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. Sm is bonded in a 12-coordinate geometry to eight Ni and nine Bi atoms. There are four shorter (3.29 Å) and four longer (3.60 Å) Sm–Ni bond lengths. There are a spread of Sm–Bi bond distances ranging from 3.45–3.61 Å. There are two inequivalent Ni sites. In the first Ni site, Ni is bonded in a 9-coordinate geometry to four equivalent Sm and five Bi atoms. There are one shorter (2.53 Å) and four longer (2.65 Å) Ni–Bi bond lengths. In the second Ni site, Ni is bonded in a distorted body-centered cubic geometry to four equivalent Sm and four equivalent Bi atoms. All Ni–Bi bond lengths are 2.65 Å. There are two inequivalent Bi sites. In the first Bi site, Bi is bonded in a 5-coordinate geometry to five equivalent Sm and five Ni atoms. In the second Bi site, Bi is bonded in a 4-coordinate geometry to four equivalent Sm and four equivalent Ni atoms.

36 MATERIALS SCIENCE↗

Materials Data on NiBi by Materials Project

NiBi crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ni is bonded in a distorted body-centered cubic geometry to two equivalent Ni and six equivalent Bi atoms. Both Ni–Ni bond lengths are 2.65 Å. All Ni–Bi bond lengths are 2.75 Å. Bi is bonded in a 6-coordinate geometry to six equivalent Ni atoms.

36 MATERIALS SCIENCE↗

Materials Data on Dy(NiBi)2 by Materials Project

Dy(NiBi)2 crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. Dy is bonded in a 4-coordinate geometry to eight Ni and nine Bi atoms. There are four shorter (3.25 Å) and four longer (3.58 Å) Dy–Ni bond lengths. There are a spread of Dy–Bi bond distances ranging from 3.41–3.67 Å. There are two inequivalent Ni sites. In the first Ni site, Ni is bonded in a distorted body-centered cubic geometry to four equivalent Dy and four equivalent Bi atoms. All Ni–Bi bond lengths are 2.63 Å. In the second Ni site, Ni is bonded in a 9-coordinate geometry to four equivalent Dy and five Bi atoms. There are one shorter (2.51 Å) and four longer (2.67 Å) Ni–Bi bond lengths. There are two inequivalent Bi sites. In the first Bi site, Bi is bonded in a 4-coordinate geometry to four equivalent Dy and four equivalent Ni atoms. In the second Bi site, Bi is bonded in a 5-coordinate geometry to five equivalent Dy and five Ni atoms.

36 MATERIALS SCIENCE↗

Topological Antiferromagnetic Van der Waals Phase in Topological Insulator/Ferromagnet Heterostructures Synthesized by a CMOS-Compatible Sputtering Technique

Breaking time-reversal symmetry by introducing magnetic order, thereby opening a gap in the topological surface state bands, is essential for realizing useful topological properties such as the quantum anomalous Hall and axion insulator states. In this work, a novel topological antiferromagnetic (AFM) phase is created at the interface of a sputtered, c-axis-oriented, topological insulator/ferromagnet heterostructure—Bi 2 Te 3 /Ni 80 Fe 20 because of diffusion of Ni in Bi 2 Te 3 (Ni-Bi 2 Te 3 ). The AFM property of the Ni-Bi2Te3 interfacial layer is established by observation of spontaneous exchange bias in the magnetic hysteresis loop and compensated moments in the depth profile of the magnetization using polarized neutron reflectometry. Analysis of the structural and chemical properties of the Ni-Bi2Te3 layer is carried out using selected-area electron diffraction, electron energy loss spectroscopy, and X-ray photoelectron spectroscopy. These studies, in parallel with first-principles calculations, indicate a solid-state chemical reaction that leads to the formation of Ni=Te bonds and the presence of topological antiferromagnetic (AFM) compound NiBi 2 Te 4 in the Ni-Bi 2 Te 3 interface layer. The Neél temperature of the Ni-Bi 2 Te 3 layer is ≈ 63 K, which is higher than that of typical magnetic topological insulators (MTIs). The presented results provide a pathway toward industrial complementary metal-oxide-semiconductor (CMOS)-process-compatible sputtered-MTI heterostructures, leading to novel materials for topological quantum devices.

36 MATERIALS SCIENCE↗