Exploring higher-order topological states in van-der-Waals 2D materials

2023 Fiscal Year Final Research Report

• Project/Area Number: 21H01022
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 13020:Semiconductors, optical properties of condensed matter and atomic physics-related
• Research Institution: NTT Basic Research Laboratories
• Principal Investigator: Wakamura Taro 日本電信電話株式会社NTT物性科学基礎研究所, 量子科学イノベーション研究部, 研究主任 (60898899)
• Co-Investigator(Kenkyū-buntansha): 橋坂 昌幸 東京大学, 物性研究所, 准教授 (80550649)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 原子層物質 / トポロジカル物性 / 超伝導 / メゾスコピック物理

Outline of Final Research Achievements

In this study we explored topological van der Waals materials WTe2 and Td-MoTe2 in the thin limit via electrical transport and current fluctuation measurements. We first measured nonreciprocal transport originated from the low dimensionality of Td-MoTe2, in which the electrical resistance varies depending on the direction of the current. In the superconducting state, we successfully observed giant nonreciprocal signals, which are one of the largest values ever reported. We next investigated the relation between the thickness, carrier density, mobility, residual resistivity ratio and the critical temperature, and discussed a possible superconducting pairing symmetry. We also performed current fluctuation measurements in WTe2. Current fluctuations are standard deviations of the current, and relevant to scattering of carriers inside the material. While current fluctuations are almost unexplored in van der Waals materials, we could observe them in bulk WTe2.

Free Research Field

物性物理学

Academic Significance and Societal Importance of the Research Achievements

本研究で用いたWTe2及びTd-MoTe2のうち、特にTd-MoTe2では超伝導とトポロジカル物性が共存するため、その超伝導特性の解明は従来の超伝導体とトポロジカル物質を接合したトポロジカル量子計算デバイスに変わる「単物質トポロジカル量子計算デバイス」の実現を前進させるものである。また、電流揺らぎ測定からは電子の散乱強度や粒子性等、通常の電気伝導測定では得られない情報を得ることが可能だが、これまで原子層物質ではほとんど行われてこなかった。本研究の実施により、今後原子層物質を始め多彩な新物質で電流揺らぎ測定を行う基板を構築することが出来、これらが有する未知の解明に貢献することが可能となった。