Hexagonal Phase Intergrown with the Tetragonal Weyl Semimetal TaAs

Abstract

TaAs as a well-known topological Weyl semimetal has attracted intense interests in recent study. Our structural investigations on the microstructure properties of TaAs samples using Cs-corrected transmission electron microscopy and scanning transmission electron microscopy evidently show the presence of a hexagonal phase intergrown with the known tetragonal TaAs (NbAs-type). The structure of the hexagonal phase is identified to have the WC-type structure (space group P6̅m2) with hexagonal c-axis along the [100]tetra or [010]tetra direction. The crystallographic correlation between the hexagonal and tetragonal phase, as well as the relevant local atomic motions, has been carefully analyzed.

Preparation of NbAs Single Crystal by the Seed Growth Process

“…In recent research on NbAs crystals, the coexistence of hexagonal and tetragonal phases was discussed. The observation or characterization of a NbAs single crystal on the atomic scale shows that the crystal is a single-phase structure [10]. In our experiments, the coexistence phase problem was overcome by improving the bottom-seed method and synthesizing the high-quality NbAs crystals with a single-phase structure, highlighting our work's significance.…”

“…NbAs is one of the first-class Weyl semimetals (TaAs, TaP, NbAs, NbP), which crystallizes in a body-centered tetragonal unit cell with lattice constants a = 3.452 Å, c = 11.679 Å, and the space group is I4 1 md(C 11 4v ) [10,11] (as shown in Figure 1a). For NbAs, the melting point of Nb reaches 2468 • C, while the As (melting point: 817 • C) has the characteristics of direct sublimation without liquefaction when heated to 613 • C under pressure.…”

Preparation of NbAs Single Crystal by the Seed Growth Process

“…In the recent research of NbAs crystals, the coexistence of hexagonal and tetragonal phases was discussed. The observation or characterization of NbAs single crystal on the atomic scale shows that the crystal is not a single phase structure [9] . In our experiments, the coexistence phase problem was overcome by improving the bottom-seed method and synthesizing the high-quality NbAs crystals with a single-phase structure, highlighting our work's significance.…”

“…) [9,10] (as shown in Figure 1(a)). For NbAs, the melting point of Nb reaches 2468 ℃, while the As (melting point: 817 ℃) has the characteristics of direct sublimation without liquefaction when heated to 613 ℃ under pressure.…”

Applications of point-contact spectroscopy in the study of topological materials

“…作者利用考虑自旋极化的s波BTK模型对数据 进行分析, 推断出TaAs表面的自旋极化率约为60%, 与 ARPES实验测量到的80%比较接近 [116] . [117] . 这样, 针尖与样品形成点接触后, 接触区域 可能是t-TaAs, h-TaAs或二者皆有.…”