Zhibo Kang, Yale University
Abstract:
Ta2NiSe5, a quasi-1D material, has been proposed to be an excitonic insulator in which exciton condensation causes a metal-to-insulator transition [1,2]. However, the putative exciton condensation is accompanied by a second-order structural phase transition, making it challenging to discern the intertwined structural and electronic instability. With the relative energy of the conduction and valence bands continuously tuned via iso-valent S-doping in Ta2Ni(Se,S)5, we show that it is strong electron-phonon coupling that dictates the broken symmetry in this system. Combining angle-resolved photo-emission spectroscopy (ARPES) and high resolution synchrotron x-ray diffraction, we tune the system across a semimetal-to-semiconductor transition, and reveal a phase diagram qualitatively different from that of an excitonic insulator in weak coupling regime [1]. Further model hamiltonian calculations reveal broad relevance of strong electron-phonon interaction beyond Born-Oppenheimer approximation in low dimensional semimetals and semiconductors.
[1] Y. Lu et al. Nat Commun 8, 14408 (2017).
[2] P. A. Volkov et al. npj Quantum Mater. 6, 52 (2021).
[3] D. Jérome et al. Excitonic insulator, Phys. Rev. 158, 462 (1967)
[4] C. Chen et al. arXiv:2203.06817
Poster Session Link: https://gather.town/invite?token=0pEoq7VP
If you have any questions for the presenter, please contact them via email: zhibo.kang@yale.edu