Superconductivity and hybrid soft modes in TiSe${}_2$

Abstract

The competition between superconductivity and other ground states of solids is one of the challenging topics in condensed matter physics. Apart from high-temperature superconductors [1,2] this interplay also plays a central role in the layered transition-metal dichalcogenides, where superconductivity is stabilized by suppressing charge-density-wave order to zero temperature by intercalation [3] or applied pressure [4-7]. 1T-TiSe${}_2$ 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 Cu${}_x$TiSe${}_2$ and pressurized 1T-TiSe${}_2$ 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-TiSe${}_2$ under pressure is close to the elusive state of the excitonic insulator.

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Cited by in corpus (2)

• Effect of Cu intercalation and pressure on excitonic interaction in 1T-TiSe2
• Electron-phonon coupling and superconductivity-induced distortion of the phonon lineshape in V${}_3$Si