• Letter

Spin-gap formation due to spin-Peierls instability in π-orbital-ordered NaO2

Mizuki Miyajima, Fahmi Astuti, Takahito Fukuda, Masashi Kodani, Shinsuke Iida, Shinichiro Asai, Akira Matsuo, Takatsugu Masuda, Koichi Kindo, Takumi Hasegawa, Tatsuo C. Kobayashi, Takehito Nakano, Isao Watanabe, and Takashi Kambe
Phys. Rev. B 104, L140402 – Published 7 October 2021
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Abstract

We have investigated the low-temperature magnetism of sodium superoxide (NaO2), in which spin, orbital, and lattice degrees of freedom are closely entangled. The magnetic susceptibility shows anomalies at T1=220 K and T2=190 K, which correspond well to the structural phase transition temperatures, and a sudden decrease below T3=34 K. At 4.2 K, the magnetization shows a clear stepwise anomaly around 30 T with a large hysteresis. In addition, the muon spin relaxation experiments indicate no magnetic phase transition down to T=0.3 K. The inelastic neutron scattering spectrum exhibits magnetic excitation with a finite energy gap. These results confirm that the ground state of NaO2 is a spin-singlet state. To understand this ground state in NaO2, we performed Raman scattering experiments. All the Raman-active libration modes expected for the marcasite phase below T2 are observed. Furthermore, we find that several new peaks appear below T3. This directly evidences the low crystal symmetry, namely, the presence of the phase transition at T3. We conclude that the singlet ground state of NaO2 is due to the spin-Peierls instability.

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  • Received 19 June 2021
  • Revised 16 August 2021
  • Accepted 23 September 2021

DOI:https://doi.org/10.1103/PhysRevB.104.L140402

©2021 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Mizuki Miyajima1,*,†, Fahmi Astuti2,3,*,‡, Takahito Fukuda1, Masashi Kodani1, Shinsuke Iida4, Shinichiro Asai4, Akira Matsuo4, Takatsugu Masuda4,5,6, Koichi Kindo4, Takumi Hasegawa7, Tatsuo C. Kobayashi1, Takehito Nakano8, Isao Watanabe2,3, and Takashi Kambe1,§

  • 1Department of Physics, Okayama University, Okayama 700-8530, Japan
  • 2Advanced Meson Science Laboratory, RIKEN Nishina Center, Wako, Saitama 351-0198, Japan
  • 3Department of Physics, Hokkaido University, Sapporo 060-0808, Japan
  • 4Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
  • 5Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801, Japan
  • 6Trans-scale Quantum Science Institute, University of Tokyo, Tokyo 113-0033, Japan
  • 7Graduate School of Advanced Science and Engineering, Hiroshima University, Higashi-Hiroshima, 739-8521, Japan
  • 8Institute of Quantum Beam Science, Ibaraki University, Mito, Ibaraki 310-8512, Japan

  • *These authors contributed equally to this work.
  • Present address: Institute for Molecular Science, Okazaki, Japan.
  • Present address: Department of Physics, Institut Teknologi Sepuluh Nopember, Indonesia.
  • §Corresponding author: kambe@science.okayama-u.ac.jp

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Issue

Vol. 104, Iss. 14 — 1 October 2021

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