Raman scattering study of large magnetoresistance semimetals TaAs2 and NbAs2.

We have performed polarized and temperature-dependent Raman scattering measurements on extremely large magnetoresistance compounds TaAs2 and NbAs2. In both crystals, all the Raman active modes, including six Ag modes and three Bg modes, are clearly observed and well assigned with the combination of symmetry analysis and first-principles calculations. The well-resolved periodic intensity modulations of the observed modes with rotating crystal orientations verify the symmetry of each assigned mode and are fitted to experimentally determine the elements of Raman tensor matrices. The broadening of two Ag modes seen in both compounds allows us to estimate the electron-phonon coupling constant, which suggests a relatively small electron-phonon coupling in the semimetals TaAs2 and NbAs2. The present study provides the fundamental lattice dynamics information on TaAs2 and NbAs2 and may shed light on the understanding of their extraordinary large magnetoresistance. [ABSTRACT FROM AUTHOR]