The interplay between superconductivity and charge-density-wave (CDW) order plays a central role in the layered transition-metal dichalcogenides. 1T−TiSe2 forms a prime example, featuring superconducting domes on intercalation as well as under applied pressure. Here, we present high energy-resolution inelastic x-ray scattering measurements of the CDW soft phonon mode in intercalated CuxTiSe2 and pressurized 1T−TiSe2 along with detailed ab-initio calculations for the lattice dynamical properties and phonon-mediated superconductivity. We find that the intercalation-induced superconductivity can be explained by a solely phonon-mediated pairing mechanism, while this is not possible for the superconducting phase under pressure. We argue that a hybridization of phonon and exciton modes in the pairing mechanism is necessary to explain the full observed temperature-pressure-intercalation phase diagram. These results indicate that 1T−TiSe2 under pressure is close to the elusive state of the excitonic insulator.
[1]
R. Sarpong,et al.
Bio-inspired synthesis of xishacorenes A, B, and C, and a new congener from fuscol† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c9sc02572c
,
2019,
Chemical science.
[2]
A. Said,et al.
Superconducting energy gap of 2H-NbSe2 in phonon spectroscopy
,
2016,
1610.00110.
[3]
W. Marsden.
I and J
,
2012
.
[4]
Tanmoy Das,et al.
Superconductivity and topological Fermi surface transitions in electron-doped cuprates near optimal doping
,
2007,
0711.1504.
[5]
Physical Review Letters 63
,
1989
.