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arXiv 1806.01276cond-mat.str-el
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分数激励磁序:对$\mathrm{Yb}_2 \mathrm{Ti}_2 \mathrm{O}_7$的应用

Magnetic Order with Fractionalized Excitations: Applications to $\mathrm{Yb}_2 \mathrm{Ti}_2 \mathrm{O}_7$

Li Ern Chern, Yong Baek Kim

摘要:

最近在$\mathrm{Yb}_2 \mathrm{Ti}_2 \mathrm{O}_7$上进行的非弹性中子散射实验揭示了尽管基态中的铁磁有序是张开的,但在自旋激发谱中仍存在不寻常的散射连续谱。在高磁场下,自旋波的激发是明确的,但随着磁场的减小,单磁振子模和双磁振子连续谱开始强烈重叠,最终在零磁场下成为散射连续谱。受这些观察的启发,我们研究了可能出现的磁有序基态的自旋模型与交换参数从以前的两个实验确定的分数激发。利用费米子部分子平均场论,我们证明了在足够强的量子涨落存在下,具有分数激发的磁有序态可以作为稳定的平均场基态出现。在这样的基态的自旋激发谱计算和散射连续显示。随着磁场的增加,分数化的磁有序态被抑制,并最终被高场下的常规磁有序相所取代,这与实验数据一致。我们讨论了进一步的影响,这些结果的实验和可能的改进的理论分析。

英文摘要:

A recent inelastic neutron scattering experiment on $\mathrm{Yb}_2 \mathrm{Ti}_2 \mathrm{O}_7$ uncovers an unusual scattering continuum in the spin excitation spectrum despite the splayed ferromagnetic order in the ground state. While there exist well defined spin wave excitations at high magnetic fields, the one magnon modes and the two magnon continuum start to strongly overlap upon decreasing the field, and eventually they become the scattering continuum at zero field. Motivated by these observations, we investigate the possible emergence of a magnetically ordered ground state with fractionalized excitations in the spin model with the exchange parameters determined from two previous experiments. Using the fermionic parton mean field theory, we show that the magnetically ordered state with fractionalized excitations can arise as a stable mean field ground state in the presence of sufficiently strong quantum fluctuations. The spin excitation spectrum in such a ground state is computed and shown to have the scattering continuum. Upon increasing the magnetic field, the fractionalized magnetically ordered state is suppressed, and is eventually replaced by the conventional magnetically ordered phase at high fields, which is consistent with the experimental data. We discuss further implications of these results to the experiments and possible improvements on the theoretical analysis.

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