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Open Access Publications from the University of California

Hidden Order and Dimensional Crossover of the Charge Density Waves in TiSe2.

  • Author(s): Chen, P
  • Chan, Y-H
  • Fang, X-Y
  • Mo, S-K
  • Hussain, Z
  • Fedorov, A-V
  • Chou, MY
  • Chiang, T-C
  • et al.

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Charge density wave (CDW) formation, a key physics issue for materials, arises from interactions among electrons and phonons that can also lead to superconductivity and other competing or entangled phases. The prototypical system TiSe2, with a particularly simple (2 × 2 × 2) transition and no Kohn anomalies caused by electron-phonon coupling, is a fascinating but unsolved case after decades of research. Our angle-resolved photoemission measurements of the band structure as a function of temperature, aided by first-principles calculations, reveal a hitherto undetected but crucial feature: a (2 × 2) electronic order in each layer sets in at ~232 K before the widely recognized three-dimensional structural order at ~205 K. The dimensional crossover, likely a generic feature of such layered materials, involves renormalization of different band gaps in two stages.

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