Resonant Raman Spectroscopy of Davydov Components of High-Frequency A'1(A21g) Modes in Multilayer MoTe2

We systematically study the high-resolution and polarized Raman spectra of multilayer (ML) MoTe2. The layer-breathing (LB) and shear (C) modes are observed in the ultralow frequency region, which are used to quantitatively evaluate the interlayer coupling in ML-MoTe2 based on the linear chain model. The Raman spectra on three different substrates verify the negligible substrate effect on the phonon frequencies of ML-MoTe2. 10 excitation energies are used to measure the high-frequency modes of N layer MoTe2 (NL-MoTe2, N is an integer). Under the resonant excitation condition, we observe layer number dependent Davydov components in ML-MoTe2, which originating from the Raman-active A'1(A21g) modes at 172 cm-1. More than two Davydov components are observed in NL-MoTe2 for N more than 4 by Raman spectroscopy. The N-dependent Davydov components are further investigated based on the symmetry analysis and calculated by the van der Waals model. The different resonant profiles for the two Davydov components in 3L-MoTe2 indicates that proper excitation energy must be chosen to observe the Davydov splitting in ML-MoTe2. Our work reveals how the van der Waals interactions significantly affect the frequency of the high frequency intralayer phonon modes and expands the understanding on the lattice vibrations and interlayer coupling of transition metal dichalcogenides and other two-dimensional materials.