Pressure induced topological and structural phase transitions in 1T-TiSe2: a Raman study

High pressure Raman spectroscopy studies on 1T-TiSe2 were carried out up to similar to 20.5 GPa. Based on the anomalies in phonon line width (lifetime) and phonon frequency of A(1g) mode, we observe three transitions at similar to 2.5 GPa, similar to 6.0GPa and similar to 15 GPa. The transitions at similar to 2.5 and similar to 6.0GPa are the two topological phase transitions consistent with the theoretical prediction by Zhu et al in 1T-TiSc2 under pressure, namely, a topological trivial to non-trivial transition (Z(2) = 1) and topological non-trivial to trivial transition (Z(2) = 0). The trigonal (1T) phase of TiSe2 is stable up to similar to 15 GPa beyond which it undergoes structural transition as seen from the appearance of new Raman modes. There is a coexistence of the 1T and the new high-pressure phase up to similar to 19 GPa. The structural transition is completely reversible as seen from the appearance of 1T phase Raman spectra upon release of the pressure.