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

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, Takashi Kambe

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2 Citations (Scopus)


We have investigated the low-temperature magnetism of sodium superoxide (), in which spin, orbital, and lattice degrees of freedom are closely entangled. The magnetic susceptibility shows anomalies at  K and  K, which correspond well to the structural phase transition temperatures, and a sudden decrease below  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  K. The inelastic neutron scattering spectrum exhibits magnetic excitation with a finite energy gap. These results confirm that the ground state of is a spin-singlet state. To understand this ground state in , we performed Raman scattering experiments. All the Raman-active libration modes expected for the marcasite phase below are observed. Furthermore, we find that several new peaks appear below . This directly evidences the low crystal symmetry, namely, the presence of the phase transition at . We conclude that the singlet ground state of is due to the spin-Peierls instability.

Original languageEnglish
Article numberL140402
JournalPhysical Review B
Issue number14
Publication statusPublished - 1 Oct 2021
Externally publishedYes


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