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arXiv 2107.01783cond-mat.str-el
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$π$ -轨道有序NaO $_2$中自旋Peierls不稳定性引起的自旋能隙形成

Spin-gap formation due to spin-Peierls instability in $π$-orbital-ordered NaO$_2$

Mizuki Miyajima, Fahmi Astuti, Takahito Fukuda, Masashi Kodani, Shinsuke Iida, Shinichiro Asai, Akira Matsuo, Takatsugu Masuda, Koichi Kindo, Takumi Hasegawa, T… 展开作者

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

摘要:

我们研究了超氧化钠(NaO $_{2}$)的低温磁性,其中自旋、轨道和晶格自由度紧密纠缠。磁化率在$T_{1}=220$ K和$T_{2}=190$ K处出现异常,与结构相变温度相对应,在低于$T_{3}=34$ K时磁化率突然下降。在4.2 K时,磁化强度在30 T附近显示出明显的阶梯状异常,并具有较大的磁滞。此外,μ子自旋弛豫实验表明,在低至$T=0.3$ K时没有磁相变。非弹性中子散射谱表现出有限能隙的磁激发。这些结果证实了NaO $_{2}$的基态是自旋单重态。为了理解NaO $_{2}$的基态,我们进行了拉曼散射实验。观察到了低于$T_{2}$的白铁矿相的所有拉曼活性振动模式。此外,我们发现几个新的峰出现在$T_{3}$之下。这直接证明了低晶体对称性,即在$T_{3}$处存在相变。我们认为NaO $_{2}$的单重基态是由于自旋Peierls不稳定性引起的。

英文摘要:

We have investigated the low-temperature magnetism of sodium superoxide (NaO$_{2}$), in which spin, orbital, and lattice degrees of freedom are closely entangled. The magnetic susceptibility shows anomalies at $T_{1}=220$ K and $T_{2}=190$ K, which correspond well to the structural phase transition temperatures, and a sudden decrease below $T_{3}=34$ 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 NaO$_{2}$ is a spin-singlet state. To understand this ground state in NaO$_{2}$, we performed Raman scattering experiments. All the Raman-active libration modes expected for the marcasite phase below $T_{2}$ are observed. Furthermore, we find that several new peaks appear below $T_{3}$. This directly evidences the low crystal symmetry, namely, the presence of the phase transition at $T_{3}$. We conclude the singlet-ground state of NaO$_{2}$ due to the spin-Peierls instability.

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