Vibrational properties of layered BiTeCl single crystal

Abstract Bismuth tellurohalides have intrigued numerous interests for their novel Rashba splitting electronic structures with potential applications in spintronics and two‐dimensional (2D) optoelectronics. In this work, we have a detailed study of bulk BiTeCl and its exfoliated flakes using ultralow wavenumber Raman spectroscopy. We observe all BiTeCl characteristic Raman modes including the lowest wavenumber rigid layer in‐plane vibrational mode E 3 2 at 19 cm −1 . From 77 to 300 K, hardening of Raman modes are observed with sharpened profiles. Temperature coefficients of Raman modes except E 3 2 are around −0.009 to −0.027 cm −1 /K, showing the sensitive response of lattice vibrations to temperature, whereas E 3 2 has a much smaller temperature coefficient of −0.004 cm −1 /K and almost constant linewidth, similar to the behavior of shear mode of 2D materials. Furthermore, by using excitation lasers of 488, 514.5, 647, and 785 nm, we find that BiTeCl Raman modes are nondispersive, 2 characteristic in‐plane E modes are more pronounced for low‐energy lasers whereas out‐of‐plane A 1 modes behave inversely, which could be related to the interband transitions. Our work provides valuable lattice vibrational and thermal information of BiTeCl for its integration into the emerging 2D nano devices as a promising polar layered material.