Lattice vibrations in the orthorhombic commensurate charge density wave phase of 2H-TaSe 2

Abstract

Lattice vibrations in 2H-TaSe 2 have been reinvestigated by Raman scattering in view of the recent orthorhombic structure of the commensurate charge density wave (CCDW) phase. The renormalization of six charge density waves on two layers gives four A g modes and two B 1g modes in the orthorhombic CCDW phase, in place of two A 1g modes and two E 2g modes in the hexagonal CCDW phase which had been believed. The splitting of the E 2g modes to the A g and B 1g modes in the orthorhombic symmetry depends on the interlayer interaction. The observed small splitting less than 3 cm -1 shows the weak interlayer interaction. The energies of the four A g modes and the two B 1g modes are presented as a function of temperature.