Detection of higher-order spin and orbital degrees of freedom through novel polarized neutron scattering techniques

2018 Fiscal Year Final Research Report

• Project/Area Number: 16H04007
• 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: Tohoku University
• Principal Investigator: Nambu Yusuke 東北大学, 金属材料研究所, 准教授 (60579803)
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: 物性実験 / 中性子散乱 / 鉄系超伝導 / フラストレート磁性 / スピントロニクス

Outline of Final Research Achievements

We have conducted the following research topics. (1) In iron-based ladder compound BaFe2Se3 which shows superconductivity under pressures, an orbital order is elucidated. Polar state is identified in BaFe2Se3 through a detailed determination of the space group. Dynamical magnetism in these compounds is examined by combining neutrons and muons, and characteristic timescale of spin fluctuations spanning eight orders in magnitude is quantitatively measured. (2) For the triangular antiferromagnet NiGa2S4, magnetic quadrupole correlation was clarified from neutron and Raman scattering experiments. We also elucidated the vector chirality-driven anomaly at 8.5 K through polarized neutron scattering. (3) We discovered the magnon polarization in the spintronics material Y3Fe5O12.

Free Research Field

物性物理学

Academic Significance and Societal Importance of the Research Achievements

磁気四重極子、カイラリティ、軌道揺らぎ等の高次スピン自由度および軌道自由度に基づく物性は磁性研究の分野で注目されており、実験的証拠は蓄積されているものの、その直接検出が待望されてきた。例えば、中性子散乱は二点相関関数を検出するため、磁気散乱で観測できるのはスピンスピン相関のみに限られる。それゆえスピン自由度が担う相関と素励起の観測には威力を発揮してきたが、高次スピン自由度および軌道自由度については現行の手法では傍証しか得ることしかできなかった。本研究で得られた新しい中性子散乱手法とその他の実験による観測は電子の新奇自由度の理解を深め、他の自由度への波及効果という点でも意義深いと考えられる。