Andreev and Majorana bound states sutudied in topological Josephson junction

2022 Fiscal Year Final Research Report

• Project/Area Number: 19H00867
• Research Category: Grant-in-Aid for Scientific Research (A)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Medium-sized Section 29:Applied condensed matter physics and related fields
• Research Institution: Institute of Physical and Chemical Research
• Principal Investigator: Ishibashi Koji 国立研究開発法人理化学研究所, 開拓研究本部, 主任研究員 (30211048)
• Project Period (FY): 2019-04-01 – 2022-03-31
• Keywords: アンドレーエフ束縛状態 / マヨラナ束縛状態 / 半導体ナノワイア / 2次元トポロジカル絶縁体 / ジョセフソン接合 / ２次元物質

Outline of Final Research Achievements

The goal of the project is to realize Josephson junctions with a InAs nanowires and monolayer WTe2 that is confirmed to be a 2-dimensional topological insulator. In the trivial condition, the Andreev bound states are formed while in the topological conditions, the Majorana bound states are predicted to be formed. Energy spectrum of the bound states have a 2pai periodicity for the former case, but they are predicted to have a 4pai periodicity for the latter case.
In the project, we have developed techniques to fabricate InAs Josephson junctions with a hard gap (clean and sharp interfaces). We have developed the unique flip chip technique to realize couplings between the Josephson junction and the microwave circuit resonator, and could measure the energy spectrum of the Andreev bound state in the InAs nanowire Josephson junction. By developing a method to form a good superconducting contacts, we have succeed in fabricating Josephson junctions both in multi-layer and mono-layer WTe2.

Free Research Field

ナノデバイス工学

Academic Significance and Societal Importance of the Research Achievements

本研究は長期的にはトポロジカル超伝導体に発現するマヨラナ量子状態の観測を目指した研究である。マヨラナ量子状態はトポロジカル量子ビットとして用いることができ、コヒーレンスに優れていることが理論的に指摘されているため、量子コンピュータの性能向上に有効である。マヨラナ量子状態はいまだ発見されていないが、量子ビット応用に適したデバイス構造である半導体ナノワイアや2次元トポロジカル絶縁体においてそれが観測されることの意義は大きい。本研究成果は、それに向けた具体的な実験的第１歩であるといえる。