Comunicazione
Raman study of charge-density-wave phase transitions in $1T$ - $TaSe_{2}$.
Ruggeri M., Sayers C., Romano V., D'Angelo G.
Charge density wave (CDW) refers to the periodic modulation of electronic distributions accompanied by the lattice distortion. The capacity to control collective electron states is a main issue of materials research since may allow for the development of novel devices. Transition-metal dichalcogenides (TMDs) $MX2 (M= Ti, Nb, Ta; X$= S, Se, Te)$ exhibit a rich collection of charge density wave phases which coexist or compete with superconductivity. Though intensively studied, the mechanisms of CDWs and superconductivity in TMDs are still under debate. Here we have performed systematic in situ low-temperature Raman measurements and angle-resolved Raman scattering study on tantalum diselenide ($1T$-$TaSe_{2}$) to identify the phonons involved in the CDWs phase. The lattice distortion associated to the CDW phase coincides with new Raman peaks resulting from zone-folding of phonon modes from middle regions of the original Brillouin zone back to $\Gamma$. Furthermore, combining the obtained polarization data with DFT calculations, we were able to assign the vibrational symmetry of the Raman-active modes to each observed phonon mode.