Strong and Tunable Electrical Anisotropy in Type-II Weyl Semimetal Candidate WP<sub>2</sub> with Broken Inversion Symmetry.
basic_science · Level V
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- Also identified by DOI 10.1002/adma.201903498.
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Abstract
A transition metal diphosphide, WP<sub>2</sub> , 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 WP<sub>2</sub> , spatial inversion symmetry breaking in this compound has rarely been investigated. Furthermore, the anisotropy of the WP<sub>2</sub> 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 WP<sub>2</sub> 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 WP<sub>2</sub> . Moreover, the measured ratio (R<sub>c</sub> /R<sub>a</sub> ) 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 R<sub>c</sub> /R<sub>a</sub> of WP<sub>2</sub> 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 WP<sub>2</sub> 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.