Unconventional charge-density-wave transition in monolayer 1T-TiSe2

Katsuaki Sugawara, Yuki Nakata, Ryota Shimizu, Patrick Han, Taro Hitosugi, Takafumi Sato, Takashi Takahashi

Research output: Contribution to journalArticlepeer-review

123 Citations (Scopus)


Reducing the dimension in materials sometimes leads to unexpected discovery of exotic and/or pronounced physical properties such as quantum Hall effect in graphene and high-Temperature superconductivity in iron-chalcogenide atomically thin films. Transition-metal dichalcogenides (TMDs) provide a fertile ground for studying the interplay between dimensionality and electronic properties, since they exhibit a variety of electronic phases like semiconducting, superconducting, and charge-densitywave (CDW) states. Among TMDs, bulk 1T-TiSe2 has been a target of intensive studies due to its unusual CDW properties with the periodic lattice distortions characterized by the three-dimensional (3D) commensurate wave vector. Clarifying the ground states of its two-dimensional (2D) counterpart is of great importance not only to pin down the origin of CDW, but also to find unconventional physical properties characteristic of atomic-layer materials. Here, we show the first experimental evidence for the realization of 2D CDW phase without Fermi-surface nesting in monolayer 1T-TiSe2. Our angle-resolved photoemission spectroscopy (ARPES) signifies an electron pocket at the Brillouin-zone corner above the CDW-Transition temperature (TCDW ∼ 200 K), while, below TCDW, an additional electron pocket and replica bands appear at the Brillouin-zone center and corner, respectively, due to the back-folding of bands by the 2 × 2 superstructure potential. Similarity in the spectral signatures to bulk 1T-TiSe2 implies a common driving force of CDW, i.e., exciton condensation, whereas the larger energy gap below TCDW in monolayer 1T-TiSe2 suggests enhancement of electron-hole coupling upon reducing dimensionality. The present result lays the foundation for the electronic-structure engineering based with atomic-layer TMDs.

Original languageEnglish
Pages (from-to)1341-1345
Number of pages5
JournalACS Nano
Issue number1
Publication statusPublished - 2016 Jan 26


  • 1T-TISE2
  • Angle-resolved photoemission spectroscopy
  • Charge density wave
  • Electronic states
  • Scanning tunneling microscopy
  • Transition-metal dichalchogenides


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