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Fig. (a) Calculation of the enthalpies of various possible structural phases at high pressure for TaAs crystals; (b) Structurally predicted TaAs unit cell volume-pressure curves; (c) TaAs high pressure hexagonal phase P-6m2 first Brillouin zone Schematic representation of the distribution of the Outer Point; (d) Insulation-to-metal transition temperature TM-I, curves for 1.8K and 300K resistances with pressure in TaAs single crystals; (e) Isotherm (4.5K) magnetization for TaAs single crystals at different pressures The resistance curve, where the dashed line represents the linear fitting result, and the arrow represents the characteristic magnetic field deviating from the linear behavior.
Yang Zhaorong, Research Fellow of the Strong Magnetic Field Science Center of the Chinese Academy of Sciences, Hefei Institute of Material Science, and professors Sun Jing, Wan Xiangang of Nanjing University, and Yang Wenge, a researcher of the Beijing High-Pressure Research Center, and others, the quantum sequence of TaAs in the topological semi-metal material New progress has been made in the research of regulation and control. The relevant results were published in the Physical Review Letter in the Press-Induced New Topological Weyl Semimetal Phase in TaAs.
With the discovery of topological insulators, the topological properties of materials and novel quantum effects have received extensive attention and research in the past decade. The family of topological electronic materials has also gradually expanded from the original topological insulators to Dirac semimetals and MOSFETs. Metal and so on. With the novel physical properties such as the Fermi-arc in the surface state and the negative magnetoresistance due to the anomalous chirality, we have potential applications in low-energy electronic devices and quantum computing. In 2015, the TaAs family with non-central symmetry was predicted by theory and became the first field-proven semi-metallic system. This type of material has a tetragonal structure under normal pressure, and its three-dimensional Brillouin zone contains 24 outliers. At two different energy levels. As a clean dimension, pressure acts directly on the degree of lattice freedom and is a direct way to regulate quantum phase transitions and induce new states of matter. Therefore, how the topological characteristics of materials under pressure not only contributes to the study of the physical nature of Forge semimetals, but also provides new ideas for the design of new topological electronic materials.
The research team conducted a detailed study on the physical behavior of TaAs single crystal at high pressure through theoretical analysis combined with high-voltage electrical transport measurements and synchrotron radiation X-ray diffraction (pressure up to 54 GPa). Theoretical predictions and experimental measurements consistently show that the 24 Outer points at two different energy levels in the TaAs normal pressure tetragonal I41md structure can be stably present in the low pressure region. When the pressure exceeds 14 GPa, a new high pressure hexagonal phase P-6m2 appears. Further studies have found that the high-pressure hexagonal phase belongs to a new type of topological semimetal, which has only 12 outliers and is located above the same energy level, and therefore has a simpler band structure compared to the normal pressure phase. The X-ray diffraction experimental results of synchrotron radiation under pressure relief demonstrate that the novel topological semimetal phase can be stably retained to atmospheric pressure, which provides the possibility for further study of the new semi-metal phase at atmospheric pressure.
The electrical transmission measurement under high pressure was performed on a high-pressure, strong magnetic field, and low temperature integrated measurement system in the center of a strong magnetic field. Strong magnetic field center assistant researcher Zhou Yonghui, doctoral students Lu Pengchao and Du Yongping of Nanjing University, and Zhu Xiangde, associate researcher of the strong magnetic field center, were the co-first authors. The above research results were funded by the National Natural Science Foundation of China and the “973†project. The work cooperation unit also includes Hefei Research Institute of Solid State Physics, Chinese Academy of Argonne National Laboratory and Nanjing University Collaborative Innovation Center.
Paper Information: Pressure-Induced New Topological Weyl Semimetal Phase in TaAs, Phys. Rev. Lett. 117(14), 146402 (2016). doi: 10.1103/PhysRevLett.117.146402.
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