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<p>Trions, three-body bound states composed of an exciton and an additional charge, are typically fragile and require external excitation to form. Here, we report the spontaneous emergence of stable trions at the surface of the layered semiconductor Ta<sub>2</sub>NiS<sub>5</sub>, revealed through angle-resolved photoemission spectroscopy. We observe a sharp, highly localized in-gap feature that cannot be explained by conventional band-theory. Instead, we argue that it arises from the formation of negative trions, stabilized by surface-induced band bending and the material’s quasi-one-dimensional geometry. Unlike excitons, these trions form without optical pumping and persist at equilibrium, marking a rare example of an interaction-driven surface state in a nominally conventional semiconductor. Our findings establish Ta<sub>2</sub>NiS<sub>5</sub> as a unique platform for exploring many-body physics at surfaces and open new avenues for studying and controlling collective excitations in low-dimensional systems.</p>

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Equilibrium trions on the surface of Ta2NiS5

  • 期刊论文

  • 出版模式：

    开放获取

  • 发表日期：

    2026年7月30日

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  • Yuval Nitzav,
  • Abigail Dishi,
  • Himanshu Lohani,
  • Ittai Sidilkover,
  • Noam Ophir,
  • Roni Anna Gofman,
  • Avior Almoalem,
  • Ilay Mangel,
  • Nitzan Ragoler,
  • Francois Bertran,
  • Jaime Sánchez-Barriga,
  • Dmitry Marchenko,
  • Andrei Varykhalov,
  • Nicholas Clark Plumb,
  • Irena Feldman,
  • Hadas Soifer,
  • Anna Keselman,
  • Amit Kanigel

摘要

Trions, three-body bound states composed of an exciton and an additional charge, are typically fragile and require external excitation to form. Here, we report the spontaneous emergence of stable trions at the surface of the layered semiconductor Ta2NiS5, revealed through angle-resolved photoemission spectroscopy. We observe a sharp, highly localized in-gap feature that cannot be explained by conventional band-theory. Instead, we argue that it arises from the formation of negative trions, stabilized by surface-induced band bending and the material’s quasi-one-dimensional geometry. Unlike excitons, these trions form without optical pumping and persist at equilibrium, marking a rare example of an interaction-driven surface state in a nominally conventional semiconductor. Our findings establish Ta2NiS5 as a unique platform for exploring many-body physics at surfaces and open new avenues for studying and controlling collective excitations in low-dimensional systems.