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arXiv 2006.15554cond-mat.str-el
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自旋为1/2的近海森堡三角形反铁磁体Ba3CoSb2O9中准粒子衰变的避免和激发连续谱的增强

Avoided quasiparticle decay and enhanced excitation continuum in the spin-1/2 near-Heisenberg triangular antiferromagnet Ba3CoSb2O9

David Macdougal, Stephanie Williams, Dharmalingam Prabhakaran, Robert I. Bewley, David J. Voneshen, Radu Coldea

摘要:

利用单晶高分辨非弹性中子散射研究了自旋为1/2的三角形反铁磁体Ba 3CoSb 2 O 9在120度有序相中的磁激发。与线性自旋波理论相比,在整个倒易空间中观察到没有衰变的尖锐磁振子,具有强重整化色散和多个软模式。我们提出了一个经验参数化,可以定量地捕获在三维布里渊区的完整的色散,并明确表明,色散重整化有直接的后果,一个到两个磁振子衰变是避免整个倒易空间,而这种衰变将被允许的非重整化色散。在更高的能量,我们观察到一个非常强的连续激发与高度结构化的强度调制扩展到至少4倍的最大单磁振子能量。单磁振子强度在增加能量时的下降速度比线性自旋波理论所预测的要快得多,并且高能连续谱包含的强度比双磁振子截面所能解释的要多得多,这表明光谱重量从高能磁振子转移到高能连续谱态。我们属性的强色散重正化和大量转移的光谱重量连续态的量子涨落和相互作用超出自旋波近似的效果,并连接到理论方法,可能会捕捉到这样的效果。最后,通过测量在一个强的外加磁场中,我们发现在120度有序的基态的自旋旋转相反的意义的磁畴的证据,如预期的Dzyaloshinskiiii-Moriya相互作用的情况下,自旋旋转的意义是通过自发对称性破缺选择。

英文摘要:

We explore the magnetic excitations of the spin-1/2 triangular antiferromagnet Ba3CoSb2O9 in its 120 degree ordered phase using single-crystal high-resolution inelastic neutron scattering. Sharp magnons with no decay are observed throughout reciprocal space, with a strongly renormalized dispersion and multiple soft modes compared to linear spin wave theory. We propose an empirical parametrization that can quantitatively capture the complete dispersions in the three-dimensional Brillouin zone and explicitly show that the dispersion renormalizations have the direct consequence that one to two magnon decays are avoided throughout reciprocal space, whereas such decays would be allowed for the unrenormalized dispersions. At higher energies, we observe a very strong continuum of excitations with highly-structured intensity modulations extending up at least 4x the maximum one-magnon energy. The one-magnon intensities decrease much faster upon increasing energy than predicted by linear spin wave theory and the higher-energy continuum contains much more intensity than can be accounted for by a two-magnon cross-section, suggesting a significant transfer of spectral weight from the high-energy magnons into the higher-energy continuum states. We attribute the strong dispersion renormalizations and substantial transfer of spectral weight to continuum states to the effect of quantum fluctuations and interactions beyond the spin wave approximation, and make connections to theoretical approaches that might capture such effects. Finally, through measurements in a strong applied magnetic field, we find evidence for magnetic domains with opposite senses for the spin rotation in the 120 degree ordered ground state, as expected in the absence of Dzyaloshinskii-Moriya interactions, when the sense of spin rotation is selected via spontaneous symmetry breaking.

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