Terahertz parametric amplification as a reporter of exciton condensate dynamics

Abstract

Condensates are a hallmark of emergence in quantum materials with superconductors and charge density wave as prominent examples. An excitonic insulator (EI) is an intriguing addition to this library, exhibiting spontaneous condensation of electron-hole pairs. However, condensate observables can be obscured through parasitic coupling to the lattice. Time-resolved terahertz (THz) spectroscopy can disentangle such obscurants through measurement of the quantum dynamics. We target $T{a}_{2}NiS{e}_5$, a putative room-temperature EI where electron-lattice coupling dominates the structural transition ($T_c$=326 K), hindering identification of excitonic correlations. A pronounced increase in the THz reflectivity manifests following photoexcitation and exhibits a BEC-like temperature dependence. This occurs well below the $T_c$, suggesting a novel approach to monitor exciton condensate dynamics. Nonetheless, dynamic condensate-phonon coupling remains as evidenced by peaks in the enhanced reflectivity spectrum at select infrared-active phonon frequencies. This indicates that parametric reflectivity enhancement arises from phonon squeezing, validated using Fresnel-Floquet theory and density functional calculations. Our results highlight that coherent dynamics can drive parametric stimulated emission with concomitant possibilities, including entangled THz photon generation.

arXiv comment51 pages, 14 figures, 1 table

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Cited by in corpus (10)

• A New Era of Excitonic Insulators
• Squeezed Josephson plasmons in driven YBa${}_2$Cu${}_3$O${}_{6+x}$
• Theory of time-crystalline behaviour mediated by phonon squeezing in Ta2NiSe5
• Terahertz stimulated parametric downconversion of a magnon mode in an antiferromagnet
• Collective modes and Raman response in Ta${}_2$NiSe${}_5$
• Long-lived population inversion in resonantly driven excitonic antiferromagnet
• Strong long-wavelength electron-phonon coupling in Ta${}_2$Ni(Se,S)${}_5$
• Optimizing Aperture Geometry in THz-TDS for Accurate Spectroscopy of Quantum Materials
• Variational and field-theoretical approach to exciton-exciton interactions and biexcitons in semiconductors
• Long-lived relaxation channel and exciton-phonon coupling in Ta2NiSe5 via non-degenerate pump-probe spectroscopy