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  • Letter
  • Open Access

Tunneling-tip-induced collapse of the charge gap in the excitonic insulator Ta2NiSe5

Qingyu He1,*, Xinglu Que1, Lihui Zhou1, Masahiko Isobe1, Dennis Huang1, and Hidenori Takagi1,2,3,†

  • 1Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany
  • 2Department of Physics, University of Tokyo, 113-0033 Tokyo, Japan
  • 3Institute for Functional Matter and Quantum Technologies, University of Stuttgart, 70569 Stuttgart, Germany

  • *q.he@fkf.mpg.de
  • †h.takagi@fkf.mpg.de
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Phys. Rev. Research 3, L032074 – Published 28 September, 2021

DOI: https://doi.org/10.1103/PhysRevResearch.3.L032074

Abstract

Tuning many-body electronic phases by an external handle is of both fundamental and practical importance in condensed matter science. The tunability mirrors the underlying interactions, and gigantic electric, optical and magnetic responses to minute external stimuli can be anticipated in the critical region of phase change. The excitonic insulator is one of the more exotic phases of interacting electrons, produced by the Coulomb attraction between a small and equal number of electrons and holes, leading to the spontaneous formation of exciton pairs in narrow-gap semiconductors/semimetals. The layered chalcogenide Ta2NiSe5 has been recently discussed as a candidate for the excitonic insulator, though the nature of the excitation gap that opens below Tc=328K remains hotly debated. Here, we demonstrate a drastic collapse of the excitation gap in Ta2NiSe5 and the realization of a zero-gap state by moving the tip of a cryogenic scanning tunneling microscope towards the sample surface by a few angstroms. We argue that the collapse of the gap is driven predominantly by the electrostatic charge accumulation at the surface induced by the proximity of the tip and the resultant carrier doping. The fragility of the gap in the insulating state of Ta2NiSe5 strongly suggests the gap possesses many-body character. Our results establish a reversible phase-change function based on Ta2NiSe5.

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Comments & Replies

Comment on “Tunneling-tip-induced collapse of the charge gap in the excitonic insulator Ta2NiSe5”

Dowook Kim, So Young Kim, Jun Sung Kim, Arthur P. Baddorf, An-Ping Li, and Tae-Hwan Kim
Phys. Rev. Research 6, 038001 (2024)

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Outline

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Phys. Rev. Research 3, L032074– Published 28 September, 2021
  • Received 14 May 2021
  • Revised 23 June 2021
  • Accepted 8 September 2021
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by the Max Planck Society.

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