Large Change of Interlayer Vibrational Coupling with Stacking in Mo1-xWxTe2
John A. Schneeloch, Yu Tao, Jaime Fernandez-Baca, Guangyong Xu, Despina Louca
Stacking variations in quasi-two-dimensional materials can have an important influence on material properties, such as changing the topology of the band structure. Unfortunately, the weakness of van der Waals interactions makes it difficult to compute the stacking dependence of properties, and even in a material as simple as graphite the stacking energetics remain unclear. Mo0.91W0.09Te2 is a material in which three differently-stacked phases are conveniently accessible by temperature changes: 1T', T∗d, and the reported Weyl semimetal phase Td. The transitions proceed via layer sliding, and the corresponding interlayer shear mode (ISM) is relevant not just for the stacking energetics, but for understanding the relationship between the Weyl physics and structural changes. However, the interlayer interactions of Mo0.91W0.09Te2 are not well understood, with wide variation in computed properties. We report inelastic neutron scattering of the ISM in Mo0.91W0.09Te2. The ISM energies are generally consistent with the linear chain model (LCM), as expected given the weak interlayer interaction, though there are some discrepancies from predicted intensities. However, the interlayer force constants Kx in the T∗d and 1T' phases are substantially weaker than that of Td, at 76(3)% and 83(3)%, respectively. Considering that the relative positioning of atoms in neighboring layers is approximately the same regardless of overall stacking, the change in Kx suggests that the stacking of layers beyond nearest neighbors has a substantial influence on interlayer vibrational coupling and the C55 elastic constant. These findings should elucidate the stacking energetics of Mo0.91W0.09Te2 and other van der Waals layered materials.
, Tao, Y.
, Fernandez-Baca, J.
, Xu, G.
and Louca, D.
Large Change of Interlayer Vibrational Coupling with Stacking in Mo<sub>1-x</sub>W<sub>x</sub>Te<sub>2</sub>, Physical Review B
(Accessed December 10, 2023)