In bulk form, TaSe₂ exhibits transitions between commensurate and incommensurate charge-density wave (CDW) phases, and is attracting interest for advanced device applications.  In order to explore the evolution of the groundstate CDW phase with layer number, mechanical exfoliation of bulk crystals provides few- to single-layer flakes.  In the present work, we extend our opto-thermal Raman measurements¹ on MoS₂ to include other TMDs, specifically TaSe₂ in both 1T and 2H crystallographic phases.  A novel, magneto-Raman microscope system affords measurement of low-frequency (down to 10 cm^-1) vibrational modes as a function of: temperature (100 K to 400 K), magnetic field (0 T to 9T) and laser excitation. The dependence of the observed Raman-active phonons on temperature and magnetic field will be discussed and compared with earlier results on MoS₂. Specifically, we observe the appearance of low-frequency, zone-folded modes in the CDW state, which soften with temperature similar to the higher frequency, in-plane E_2g mode. Additionally, we compare the measured magneto-Raman results to calculations using ab initio, density functional theory.

¹ACS Nano 2014 8, 986