Temperature dependence of the Raman spectra of 1T-TaS 2

Abstract

The temperature dependence of the unpolarized Raman spectra from 1T-TaS 2 has been measured between 297 K and 48 K. The present work demonstrates that the three Raman modes observed above 220 cm −1 (high frequency region) at room temperature exhibit remarkable frequency changes toward low wavenumbers in the vicinity of 200 K, where 1T-TaS 2 undergoes a first-order transition of the charge density wave (CDW) from nearly commensurate to a commensurate state. The monotonic line-broadening and intensity reduction with temperature has been identified for these Raman modes. In contrast, the behavior observed in the low frequency region (less than 200 cm −1), suggested that the soft phonons are less likely to be involved in the temperature dependence of the high frequency Raman modes.