Coherent order parameter oscillations in the ground state of the excitonic insulator Ta2NiSe5

Daniel Werdehausen, Tomohiro Takayama, Marc Höppner, Gelon Albrecht, Andreas W. Rost, Yangfan Lu, Dirk Manske, Hidenori Takagi, Stefan Kaiser*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

59 Citations (Scopus)
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Abstract

The excitonic insulator is an intriguing electronic phase of condensed excitons. A prominent candidate is the small bandgap semiconductor Ta2NiSe5, in which excitons are believed to undergo a Bose-Einstein condensation-like transition. However, direct experimental evidence for the existence of a coherent condensate in this material is still missing. A direct fingerprint of such a state would be the observation of its collective modes, which are equivalent to the Higgs and Goldstone modes in superconductors. We report evidence for the existence of a coherent amplitude response in the excitonic insulator phase of Ta2NiSe5. Using nonlinear excitations with short laser pulses, we identify a phonon-coupled state of the condensate that can be understood as a novel amplitudemode. The condensate density contribution substantiates the picture of an electronically driven phase transition and characterizes the transient order parameter of the excitonic insulator as a function of temperature and excitation density.

Original languageEnglish
Article numbereaap8652
Number of pages7
JournalScience Advances
Volume4
Issue number3
DOIs
Publication statusPublished - 23 Mar 2018

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