Exploration of novel quantum phenomena in non-Kramers Pr compounds by NMR

2020 Fiscal Year Final Research Report

• Project/Area Number: 17H02918
• 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: The University of Tokyo
• Principal Investigator: Masashi Takigawa 東京大学, 物性研究所, 教授 (10179575)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: 核磁気共鳴 / 多極子 / スピン軌道相互作用 / 非クラマース系Pr化合物

Outline of Final Research Achievements

In this study, we performed Al-NMR, magnetization and specific heat measurements on the caged compound PrTi2Al20, which contains non-Kramers trivalent Pr ions. We obtained a ferro-quadrupole phase diagram, which is anisotropic with respect to the magnetic field. In particular, we found discontinuous switching of the ferro-quadrupole order parameter induced by weak magnetic fields around 2 tesla along [001] and [110] directions. We proposed a physical mechanism by using a phenomenological Landau theory and model calculations, assuming competition between the magnetic Zeeman energy and the anisotropic quadrupole interactions. We also performed oxygen NMR measurements on the double perovskite compound Ba2MgReO6 and obtained sufficient data to determine the multipole order parameters of the 5d electron system.

Free Research Field

核磁気共鳴法を用いた強相関電子系の量子現象の研究

Academic Significance and Societal Importance of the Research Achievements

カゴ状化合物PrTi2Al20に対する詳細な明見ＮＭＲ実験によって、非磁性の結晶場基底状態を持つ4ｆ電子系における磁場誘起の四極子相転移を始めて発見した。また対称性に基づく理論的考察によって、磁場によるぜーまエネルギーと四極子間相互作用の異方的な磁場依存性の競合がこの現象の原因となっている可能性を指摘し、非クラマース系の理解の発展に貢献した。さらに研究対象を拡大して、二重ペロブスカイト化合の酸素サイトＮＭＲに行うことにより、5ｄ電子系における多極子秩序研究の進展に貢献した。