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 (15)

• Exciton-phonon cooperative mechanism of the triple-$q$ charge-density-wave and antiferroelectric electron polarization in TiSe${}_2$
• Competing soft phonon modes at the charge-density-wave transitions in DyTe${}_3$
• Effect of Cu intercalation and pressure on excitonic interaction in 1T-TiSe2
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• Correlation between electronic and structural orders in 1T-TiSe2
• Introduction to High-Resolution Inelastic X-Ray Scattering
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• Charge-density-wave quantum critical point under pressure in 2$H$-TaSe${}_2$
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• Optical amplification in a CDW-phase of a quasi-two dimensional material
• Unveiling Excitonic Insulator Signatures in Ta${}_2$NiSe${}_5$