Unconventional nature of superconducting NbSe2 atomic layers

2023 Fiscal Year Final Research Report

• Project/Area Number: 22K20362
• Research Category: Grant-in-Aid for Research Activity Start-up
• Allocation Type: Multi-year Fund
• Review Section: 0202:Condensed matter physics, plasma science, nuclear engineering, earth resources engineering, energy engineering, and related fields
• Research Institution: Institute of Physical and Chemical Research
• Principal Investigator: Masahiro Naritsuka 国立研究開発法人理化学研究所, 創発物性科学研究センター, 基礎科学特別研究員 (20960173)
• Project Period (FY): 2022-08-31 – 2024-03-31
• Keywords: 超伝導 / 原子層薄膜 / ツイストロニクス / 走査型トンネル顕微鏡 / 分子線エピタキシー

Outline of Final Research Achievements

The research aimed to elucidate the effects of thinning down to atomic layers and hetero-stacking on the superconducting state of the layered superconductor NbSe2. By combining molecular beam epitaxy (MBE) and scanning tunneling microscopy spectroscopy (SI-STM), it was found that the superconductivity changes by the twist angle between NbSe2 and graphene layers, which is naturally introduces during growth. In the twisted bilayer samples, residual states were observed within the superconducting gap. The origin of these states was shown to be low-energy excitations in NbSe2, resulting from the superconducting proximity effect occurring at wave numbers where the Fermi surfaces of graphene and NbSe2 overlap.

Free Research Field

物性実験

Academic Significance and Societal Importance of the Research Achievements

本研究では、NbSe2単層膜とグラフェンのひねり積層が超伝導状態に与える影響を明らかにすることに成功した。特に、運動量空間でのフェルミ面の重なりを通した超伝導近接効果を提案しており、積層のひねり角度を変えることで超伝導状態を連続的に調節できる可能性を示唆している。超伝導ツイストロニクスと呼ぶべき本研究成果は、数多く知られる層状物質の超伝導状態に適用できる新たな知見を提供し、今後の2次元超伝導体の新たな制御方法の指針となる重要な結果といえる。