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TT: Fachverband Tiefe Temperaturen
TT 39: Correlated Electrons: Charge Order
TT 39.8: Vortrag
Mittwoch, 20. März 2024, 11:30–11:45, H 3025
Substrate tuning of transition temperature in thin flakes of the excitonic insulator candidate Ta2NiSe5 — •Yuanshan Zhang1, Zichen Yang1, Dennis Huang1, Matteo Minola1, Chuanlian Xiao1, Masahiko Isobe1, Bernhard Keimer1, and Hidenori Takagi1,2,3 — 1Max Planck Institute for Solid State Research, Stuttgart, Germany — 2Department of Physics, University of Tokyo, Japan — 3Institute for Functional Matter and Quantum Technologies, University of Stuttgart, Germany
The nature of the transition in Ta2NiSe5 to an insulator around 326 K remains an active debate. The discussion focuses on whether the transition is predominantly structural, as evidenced by an orthorhombic-to-monoclinic lattice transition, or electronic/excitonic, as understood through the interplay between the energy gap and excitonic binding energy. We have separated electron and phonon effects by employing thin Ta2NiSe5 flakes on both conducting Au and insulating Al2O3 substrates. Polarized Raman spectroscopy indicates that the lattice transition is largely unchanged in flakes as thin as 3 nm on Al2O3, whereas it is reduced by nearly 100 K on Au. Model analysis reveals that the underlying electronic excitation in the latter does not exhibit an excitonic instability. We discuss how the conducting substrate influences an excitonic insulator. Our findings demonstrate that the transition in Ta2NiSe5 is charge-sensitive and cannot be attributed solely to a lattice instability. The electronic/excitonic instability appears to have an energy scale of approximately 100 K.
Keywords: Excitonic insulator; 2D materials; Electron-phonon coupling; Mechanical exfoliation; Raman spectroscopy