Direct observations of spatially modulated superconductivities with ultra-low-temperature STM

2018 Fiscal Year Final Research Report

• Project/Area Number: 16K17744
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Condensed matter physics II
• Research Institution: Kanazawa University (2018); The University of Tokyo (2016-2017)
• Principal Investigator: Yoshida Yasuo 金沢大学, 数物科学系, 准教授 (10589790)
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: 超伝導 / 走査トンネル顕微鏡 / 重い電子系 / 表面物理

Outline of Final Research Achievements

We constructed ultra-low-temperature and high magnetic field scanning tunneling micrsocope to observe spatial modulations of superconducting properties in exotic superconductors. We successed to observe atomically resolved graphite surface but the resolution and noise level of the system should be improved in the future especially in the mK temperature range and at high magnetic fields. By using the other mK STM, we discovered surface-induced orbital ordering of Co 3d orbitals at the cleaved surface of a strongly correlated superconductor for the first time. Because of screened electrostatic potentials of localized 3d orbitals, this orbital ordering may not show up in bulk. However at the surface, due to the effective reduction of the electron density, the screening of the potential by conduction electrons are weak and therefore, the orbital degree of freedom is lifted and ordering occurs. This senario was confirmed by first principle calculations done with our collaborators.

Free Research Field

低温物理、表面物理

Academic Significance and Societal Importance of the Research Achievements

本研究で発見された、表面誘起の軌道秩序現象は、これまで直接的な観察が困難だった原子軌道の物理現象を直接的に視覚的に捉えた成果である。そのため、今回と同様な測定を通して、物質の機能発現に重要な役割をする、原子軌道の物理現象の理解が今後更に深まることが期待される。また、今回見つかった表面誘起の軌道秩序現象は、電子がどの原子軌道を占有するのかという、軌道の自由度を有する物質の表面においては普遍的に起こりうる現象であり、今後、超伝導や磁性との関係が明らかになれば、新たな機能を有するスマートマテリアルの開発・設計にも大いに役立つ可能性を秘めている。