Giant exciton Fano resonance in quasi-one-dimensional Ta2NiSe5

2017/02/20 by T. I. Larkin, A. N. Yaresko, D. Pröpper +12 · 7 citations
Chemistry · Engineering · Materials Science · Physics and Astronomy · #2D Materials and Applications #Atomic physics #Chemistry #Condensed matter physics #Crystal structure #Crystallography #Excited state #Exciton #Ground state #Isostructural #Organic and Molecular Conductors Research #Oscillator strength #Perovskite Materials and Applications #Phonon #Physics #Quantum mechanics #Spectral line #cond-mat.str-el

paper · pdf · doi:10.1103/physrevb.95.195144

published as Phys. Rev. B 95, 195144 (2017) · 10 pages, 7 figures

arxiv created 2017/02/20 · openalex created_date 2017/05/12 · openalex publication_date 2017/05/19 · arxiv updated 2017/05/24 · openalex updated_date 2026/08/05

Abstract

We report the complex dielectric function of the quasi-one-dimensional chalcogenide Ta₂NiSe₅, which undergoes a structural phase transition presumably associated with exciton condensation below T_c=326 K [Y. Wakisaka et al., Phys. Rev. Lett. 103, 026402 (2009); Y. F. Lu et al., Nat. Commun. 8, 14408 (2017)], and of the isostructural Ta₂NiS₅, which does not exhibit such a transition. Using spectroscopic ellipsometry, we have detected exciton doublets with pronounced Fano line shapes in both the compounds. The exciton Fano resonances in Ta₂NiSe₅ display an order-of-magnitude higher intensity than those in Ta₂NiS₅. In conjunction with prior theoretical work [E. Rashba, Sov. Phys. Semicond. 8, 807 (1975)], we attribute this observation to the giant oscillator strength of spatially extended exciton-phonon bound states in Ta₂NiSe₅. The formation of exciton-phonon complexes in Ta₂NiS₅ and Ta₂NiSe₅ is confirmed by the pronounced temperature dependence of sharp interband transitions in the optical spectra, the peak energies and widths of which scale with the thermal population of optical phonon modes. The description of the optically excited states in terms of strongly overlapping exciton complexes is in good agreement with the hypothesis of an exciton insulator ground state.

Citations

• Evidence for an Excitonic Insulator Phase in1T−TiSe2
• Temperature-dependent photoemission on1T-TiSe2: Interpretation within the exciton condensate phase model
• Cooperative dynamics in doped manganite films: Phonon anomalies in the ferromagnetic state
• Effects of Configuration Interaction on Intensities and Phase Shifts

Cited by

• Inhibition of the photoinduced structural phase transition in the excitonic insulator Ta2NiSe5
• Thermal transport signatures of the excitonic transition and associated phonon softening in the layered chalcogenide Ta2NiSe5
• Orthorhombic-to-monoclinic transition in Ta2NiSe5 due to a zone-center optical phonon instability
• Superconductivity in Nb2Pd3Te5 and Chemically-Doped Ta2Pd3Te5
• Ta2NiSe5: A candidate topological excitonic insulator with multiple band inversions
• FFLO Superconductivity Mediated by Excitonic Fluctuation in Semimetallic Ta2NiSe5
• Evolution of the electronic structure in Ta2NiSe5 across the structural transition revealed by resonant inelastic x-ray scattering