Theoretical study of superconductivity in quasiperiodic systems

2019 Fiscal Year Final Research Report

• Project/Area Number: 17K14350
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Condensed matter physics II
• Research Institution: Institute of Physical and Chemical Research
• Principal Investigator: Sakai Shiro 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, 上級研究員 (80506733)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: 準結晶 / 超伝導 / フラクタル / 準周期系 / 非従来型超伝導

Outline of Final Research Achievements

We have revealed the fundamental properties of quasicrystalline superconductors, as well as finding a new type of superconducting state in quasicrystals under a magnetic field. Quasicrystal has a regular but aperiodic arrangement of atoms, and hence no Fermi surface. On the other hand, the Bardeen-Cooper-Schrieffer (BCS) theory, which is a fundamental theory of superconductors, starts from the pairing of two electrons on the Fermi surface. Since the quasicrystal breaks this prerequisite, it may show superconducting properties different from what the BCS theory tells. In fact, through numerical simulations, we have found that some superconducting properties of quasicrystals are substantially different from those of the BCS. We have also discovered a novel type of superconducting state under a magnetic field, which accompanies a spatial modulation of the phase of the order parameter.

Free Research Field

物性理論

Academic Significance and Societal Importance of the Research Achievements

準結晶超伝導体の基本的性質を明らかにしたことは、今後の準結晶超伝導研究の土台を与える。特に、準結晶超伝導体と通常の超伝導体との物性における差異が明らかになったことは、その特徴を実験的に検出する上で重要である。また、磁場下の超伝導状態の研究を通して、準結晶がエキゾチック超伝導と呼ばれるタイプの非従来型超伝導体の候補と成り得ることを示した。更に、これらの研究によって明らかになったフラクタル的非一様性を有する超伝導状態は、今後、フラクタル構造と超伝導の協奏を研究する上での出発点となりうる。