Superconducting 3 R-Ta1+ xSe2 with Giant In-Plane Upper Critical Fields

Yuki Tanaka, Hideki Matsuoka, Masaki Nakano, Yue Wang, Sana Sasakura, Kaya Kobayashi, Yoshihiro Iwasa

Research output: Contribution to journalArticlepeer-review

16 Citations (Scopus)


Molecular-beam epitaxy (MBE) enables the stabilization of a nonequilibrium material phase, providing a powerful approach to the exploration of emergent phenomena in condensed-matter research. Here we demonstrate that one of the metallic two-dimensional (2D) materials, TaSe2, grown by MBE crystallizes into the pure 3R phase with the self-intercalated Ta atoms, 3R-Ta1+xSe2, which is thermodynamically metastable and does not exist in nature as a pure material phase. Interestingly, the thick-enough 3R-Ta1+xSe2 film exhibits a superconducting (SC) critical temperature (Tc) of 3.0 K, which is the highest among all of the polymorphs in TaSe2. Thickness-dependence measurements reveal that Tc decreases with decreasing thickness, accompanied by the development of the charge-density wave phase. The 3R-Ta1+xSe2 films exhibit large in-plane upper critical fields (Hc2) in their SC states even in the thick-enough regime, most likely due to the suppression of the interlayer hopping associated with the unique 3R stacking. Moreover, the temperature dependence of the in-plane Hc2 evolves from linear to square-root behavior with decreasing thickness, indicating crossover behavior from anisotropic three-dimensional superconductivity to 2D superconductivity. Our results unveil intriguing SC properties of metastable 3R-Ta1+xSe2 distinct from those of thermodynamically stable 2H-TaSe2, demonstrating the essential importance of the MBE-based approach to the exploration of novel quantum phenomena in 2D materials research.

Original languageEnglish
Pages (from-to)1725-1730
Number of pages6
JournalNano Letters
Issue number3
Publication statusPublished - Mar 11 2020


  • TaSe
  • Transition-metal dichalcogenide
  • molecular-beam epitaxy
  • polymorphism
  • superconductivity

ASJC Scopus subject areas

  • Bioengineering
  • General Chemistry
  • General Materials Science
  • Condensed Matter Physics
  • Mechanical Engineering


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