The
frequencies of Raman active modes of few-layer ZrS3 and
ZrSe3 and their dependence on the number of layers
have been investigated by Raman scattering spectroscopy and first-principles
calculations. We find a considerable downshift of the frequency of
the Ag
3 mode with decreasing the number of layers,
and a slight downshift of the Ag
5 mode. The
same frequency shifts are reproduced by the calculations with remarkable
accuracy. We explain the difference in the frequency shifts of the
Ag
3 and Ag
5 modes in terms
of intrachain, interchain, and interlayer force constants in simple
one-dimensional lattice models. We thus show that the large shift
of the Ag
3 mode reflects the quasi-one-dimensional
structure of ZrS3 and ZrSe3, which does not
exist in the more widely studied two-dimensional materials.
Although single-layer transition-metal dichalcogenides with novel valley functionalities are promising candidate to realize valleytronic devices, the essential understanding of valley depolarization mechanisms is still incomplete. Based on pump-probe experiments performed...
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