Quantum Melting of the Charge-Density-Wave State in1T−TiSe2

Abstract

We report a Raman scattering study of low-temperature, pressure-induced melting of the charge-density-wave (CDW) phase of $1\mathrm{T}\mathrm{\text{−}}{\mathrm{T}\mathrm{i}\mathrm{S}\mathrm{e}}_2$. Our measurements reveal that the collapse of the CDW state occurs in three stages: (i) For $P<5\mathrm{k}\mathrm{b}\mathrm{a}\mathrm{r}$, the pressure dependence of the CDW amplitude mode energies and intensities are indicative of a “crystalline” CDW regime; (ii) for $5<P<25\mathrm{k}\mathrm{b}\mathrm{a}\mathrm{r}$, there is a decrease in the CDW amplitude mode energies and intensities with increasing pressure that suggests a regime in which the CDW softens, and exhibits enhanced fluctuations; and (iii) for $P>25\mathrm{k}\mathrm{b}\mathrm{a}\mathrm{r}$, the absence of amplitude modes reveals a metallic regime in which the CDW has melted.