Studies of strongly-correlated electrons at ultralow temperatures by thermal-expansion measurements

2021 Fiscal Year Final Research Report

• Project/Area Number: 19K21842
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 13:Condensed matter physics and related fields
• Research Institution: The University of Tokyo
• Principal Investigator: Yamashita Minoru 東京大学, 物性研究所, 准教授 (10464207)
• Project Period (FY): 2019-06-28 – 2022-03-31
• Keywords: 超低温測定 / 熱膨張率 / 強相関電子系

Outline of Final Research Achievements

The purpose of this research is to develop measurement technology to extend the strongly correlated electron system research to the ultra-low temperature region (about 1 mK), which is lower than the temperature that can be reached by a commercially available dilution refrigerator. This research completed a thermal expansion measurement cell that can work even at ultra-low temperatures. A clear signal caused by the superconducting transition of CeCoIn5 was resolved at 5 mK, demonstrating the performance of the thermal-expansion cell.
At the same time, we challenged the resistivity measurement of down to ultra-low temperatures. By using a low temperature amplifier, we succeeded the resistivity measurement of YbRh2Si2, and observed the decrease in electrical resistance that seems to be related to the superconducting transition.

Free Research Field

低温物理学

Academic Significance and Societal Importance of the Research Achievements

科学研究においてより低温までの研究を行う事は熱揺らぎに隠れていた物質の本質的性質を明らかにするためには必須である。市販の冷凍機で達成可能な温度より低温の超低温領域（～1 mK）での実験には様々な実験的困難があってこれまでほとんど行われてこなかったが、本研究成果によって熱膨張率の超低温測定が実現したことで相転移をはじめとする様々な熱力学量の測定が可能になった。これは、様々な物質における超低温測定につながる成果である。