Polarized Raman Study of First-Order Phonons in Self-Flux Grown Single-Crystalline WTe 2 .

Bulk single crystals of WTe 2 were grown by the self-flux method and characterized by X-ray diffraction, polarized micro-Raman spectroscopy, and optical microscopy. All methods revealed a high crystalline quality, thus demonstrating the advantages of the growth method used as a starting base for the synthesis of high-quality 2D materials. In each main scattering configuration, we recorded a series of Raman spectra in different sample orientations achieved by rotating the sample around the incident laser beam. In addition to the well-established case of excitation along the c crystal axis, we also applied laser excitation along the a and b axes. Thus, scattering configurations were also realized in the XZ and YZ polarization planes, for which no comparative literature data have yet been established. In these experiments, two new Raman-active phonons with B 2 symmetry and frequencies of 89 cm -1 and 122 cm -1 were identified. The obtained experimental data enabled us to derive the magnitude ratios of all three tensor elements of the A 1 modes and to find their phase differences.