valence quantum criticality investigated by microscopic probes

2021 Fiscal Year Final Research Report

• Project/Area Number: 19K23417
• Research Category: Grant-in-Aid for Research Activity Start-up
• Allocation Type: Multi-year Fund
• Review Section: 0202:Condensed matter physics, plasma science, nuclear engineering, earth resources engineering, energy engineering, and related fields
• Research Institution: Tohoku University
• Principal Investigator: Taniguchi Takanori 東北大学, 金属材料研究所, 助教 (70849950)
• Project Period (FY): 2019-08-30 – 2022-03-31
• Keywords: 強相関電子系 / 量子臨界現象 / Yb化合物 / ミュオンスピン緩和 / 中性子散乱 / 重い電子系

Outline of Final Research Achievements

We focus on the candidate material YnCu4T (T = Ni, Au) with a quantum critical point derived from the valence, and have investigated the electronic properties through some experiments such as single crystal growth, basic physical properties, and muon spin relaxation method and neutron diffraction. At first, we succeeded in synthesizing large single crystals. Using this single crystal sample, a muon spin relaxation experiment was performed at the Rutherford Appleton Laboratory (ISIS) in the United Kingdom. It was clarified that the electronic state changed at the Kondo temperature in YbCu4Au, and the temperature dependence of the electrical resistance can be explained by this result. In addition, the crystal structures of YbCu4Ni and YbCu4Au were confirmed by neutron diffraction experiments at J-PARC (JRR-3), and some changes in the previously proposed crystal structures were found. These results are the basic information for considering valence quantum critical phenomena.

Free Research Field

強相関電子系

Academic Significance and Societal Importance of the Research Achievements

銅酸化物高温超伝導体や重い電子超伝導体に代表される超伝導について、多くは反強磁性スピン揺らぎの枠組みで量子臨界現象として説明されていることが多い。最近では、多極子揺らぎや強磁性揺らぎに起因する量子臨界現象の存在が指摘されており、新奇な物性探索のために盛んに研究がなされている。本研究では、電子の特徴の一つである価数に注目し、価数揺らぎと量子臨界現象の関係について調べた。そのため、まずは候補物質について単結晶合成を試み、大型のものを得ることに成功した。この成果により、多くの実験プローブを用いることにより、候補物質が示す量子臨界現象の起源を明らかにする基盤が確立した。