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Adv Mater. 2019 Sep 18:e1903498. doi: 10.1002/adma.201903498. [Epub ahead of print]

Strong and Tunable Electrical Anisotropy in Type-II Weyl Semimetal Candidate WP2 with Broken Inversion Symmetry.

Su B1,2, Song Y1,2, Hou Y1,3, Chen X1,2, Zhao J4, Ma Y3, Yang Y1,5, Guo J1,2,5, Luo J1,5,6, Chen ZG1,2,5.

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Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.
School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100190, China.
School of Materials Science and Engineering, Tianjin University of Technology, Tianjin, 300384, China.
Co-Innovation Center for New Energetic Materials, Southwest University of Science and Technology, Mianyang, Sichuan, 621010, China.
Songshan Lake Materials Laboratory, Dongguan, Guangdong, 523808, China.
Collaborative Innovation Center of Quantum Matter, Beijing, China.


A transition metal diphosphide, WP2 , is a candidate for type-II Weyl semimetals (WSMs) in which spatial inversion symmetry is broken and Lorentz invariance is violated. As one of the prerequisites for the presence of the WSM state in WP2 , spatial inversion symmetry breaking in this compound has rarely been investigated. Furthermore, the anisotropy of the WP2 electrical properties and whether its electrical anisotropy can be tuned remain elusive. Angle-resolved polarized Raman spectroscopy, electrical transport, optical spectroscopy, and first-principle studies of WP2 are reported. The energies of the observed Raman-active phonons and the angle dependences of the detected phonon intensities are consistent with results obtained by first-principle calculations and analysis of the proposed crystal symmetry without spatial inversion, showing that spatial inversion symmetry is broken in WP2 . Moreover, the measured ratio (Rc /Ra ) between the crystalline c-axis and a-axis electrical resistivities exhibits a weak dependence on temperature (T) in the temperature range from 100 to 250 K, but increases abruptly at T ≤ 100 K, and then reaches the value of ≈8.0 at T = 10 K, which is by far the strongest in-plane electrical resistivity anisotropy among the reported type-II WSM candidates with comparable carrier concentrations. Optical spectroscopy study, together with the first-principle calculations on the electronic band structure, reveals that the abrupt enhancement of the electrical resistivity anisotropy at T ≤ 100 K mainly arises from a sharp increase in the scattering rate anisotropy at low temperatures. More interestingly, the Rc /Ra of WP2 at T = 10 K can be tuned from 8.0 to 10.6 as the magnetic field increases from 0 to 9 T. The so-far-strongest and magnetic-field-tunable electrical resistivity anisotropy found in WP2 can serve as a degree of freedom for tuning the electrical properties of type-II WSMs, which paves the way for the development of novel electronic applications based on type-II WSMs.


Raman spectroscopy; first-principle calculations; in-plane electrical anisotropy; optical spectroscopy; type-II Weyl semimetal


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