Large thermoelectric response in ultra-thin films of iron-based superconductors

2019 Fiscal Year Final Research Report

• Project/Area Number: 17H02928
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Condensed matter physics II
• Research Institution: Central Research Institute of Electric Power Industry (2019); Institute of Physical and Chemical Research (2017-2018)
• Principal Investigator: Shimizu Sunao 一般財団法人電力中央研究所, 材料科学研究所, 主任研究員 (60595932)
• Co-Investigator(Kenkyū-buntansha): 塩貝 純一 東北大学, 金属材料研究所, 助教 (30734066)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: 薄膜物性 / 超伝導 / 熱電効果 / 電気化学 / 電界効果

Outline of Final Research Achievements

In this research subject, we have investigated thermoelectric properties of FeSe ultra-thin films by utilizing the strong electric field induced in the electric double layers. FeSe thin films with the thickness of ~20 nm showed the semiconducting behavior of electrical resistance, while the FeSe films became metallic with reducing the film thickness. We systematically controlled the film thickness with electrochemical etching technique and measured the temperature dependence of the resistivity and the Seebeck effect. It was found that the superconducting transition temperature was raised up to ~50 K and the Seebeck coefficient became 100 times larger, accompanying the reduction of the thickness of the FeSe films. The present results would lead to not only the understanding of the electronic properties of monolayer FeSe but also the development of novel thermoelectric materials.

Free Research Field

材料科学

Academic Significance and Societal Importance of the Research Achievements

環境からエネルギーを取り出す技術の開発が精力的に進められており、中でも、任意の場所で、また様々なスケールで発電ができる熱電発電の重要性が近年再認識されている。本研究は薄膜を用いた研究であるが、例えばインターカレーション等の手法で同様の電子状態を創り出すことができる可能性もあり、バルクにおいても高い熱電特性を実現するための指針に繋がる。また一方で、本研究は、近年非常に注目されている単層FeSeの熱電効果を初めて報告するものであり、新奇な高温超伝導状態に対する重要な知見を与えるものである。