Superconductivity and hybrid soft modes in TiSe2

• Published in: Physical review. B 2016-12, Vol.94 (21)
• Main Authors: Maschek, M, Rosenkranz, S, Hott, R, Heid, R, Merz, Michael, Zocco, D A, Said, A H, Alatas, A, Karapetrov, G, Zhu, Shan, van Wezel, Jasper, Weber, F
• Format: Article
• Language: English
• Subjects: Charge density waves; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Inelastic scattering; Intercalation; Lattice vibration; Phase diagrams; Superconductivity; Transition metal compounds; X-ray scattering
• ISSN: 2469-9950; 2469-9969
• DOI: 10.1103/PhysRevB.94.214507

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.