揭示碱金属镧系氧化物Na$_2$PrO$_3$的磁基态
Unraveling the magnetic ground-state in alkali-metal lanthanide oxide Na$_2$PrO$_3$
AI总结：
本文通过μ子自旋谱学和中子散射结合理论模拟，揭示Na$_2$PrO$_3$在约4.9 K以下形成Néel反铁磁序，其小磁矩源于晶体场与共价效应而非显著量子涨落。
摘要：
通过一套全面的μ子自旋谱学和中子散射测量，并辅以从头算和模型哈密顿量模拟，研究了Na$_2$PrO$_3$的磁基态。μSR揭示在T_N≈4.9 K以下存在Néel反铁磁序，具有一个沿c轴共线排列的小静态磁矩m_static≤0.22 μ_B/Pr。非弹性中子测量揭示了完整的晶体场激发谱，并证实Pr^4+基态波函数显著偏离与Kitaev模型相关的Γ_7极限。在T_N=4.6 K以下的有序态中观测到单磁振子和双磁振子激发，并可由基于Néel态的非线性自旋波理论很好地描述，所用磁哈密顿量具有海森堡交换J=1 meV和对称各向异性交换Γ/J=0.1，对应于XY模型。强双磁振子激发由g因子各向异性g_z/g_±=1.29解释。从能量和动量积分的非弹性中子信号中提取的涨落矩δm^2=0.57(22) μ_B^2/Pr，相对于具有平均g因子g_avg≈1.1的局域J=1/2矩的预期值有所降低。综合这些结果表明，Na$_2$PrO$_3$中的小磁矩源于晶体场和共价效应，并且该材料不表现出显著的量子涨落。
英文摘要：
A comprehensive set of muon spin spectroscopy and neutron scattering measurements supported by ab-initio and model Hamiltonian simulations have been used to investigate the magnetic ground state of Na$_2$PrO$_3$. $μ$SR reveals Néel antiferromagnetic order below $T_{\rm N}\! \sim\! 4.9$ K, with a small static magnetic moment $m_{\rm static}\!\leq \! 0.22$~$μ_{\rm B}/{\rm Pr}$ collinearly aligned along the $c-$axis. Inelastic neutron measurements reveal the full spectrum of crystal field excitations and confirm that the Pr$^{4+}$ ground state wave function deviates significantly from the $Γ_7$ limit relevant to the Kitaev model. Single and two magnon excitations are observed in the ordered state below $T_N=4.6$ K and are well described by non-linear spin wave theory from the Néel state using a magnetic Hamiltonian with Heisenberg exchange $J=1$ meV and symmetric anisotropic exchange $Γ/J=0.1$, corresponding to an XY model. Intense two magnon excitations are accounted for by $g$-factor anisotropy $g_\mathrm{z}/g_\pm = 1.29$. A fluctuating moment $δm^2 = 0.57(22)$ $μ_{\rm B}^2/{\rm Pr}$ extracted from the energy and momentum integrated inelastic neutron signal is reduced from expectations for a local $J=1/2$ moment with average $g$-factor $g_{\rm avg}\approx 1.1$. Together, the results demonstrate that the small moment in Na$_2$PrO$_3$ arises from crystal field and covalency effects and that the material does not exhibit significant quantum fluctuations..
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