Chern Li Ern, Kim Yong Baek
Department of Physics, University of Toronto, Toronto, Ontario, M5S 1A7, Canada.
Canadian Institute for Advanced Research/Quantum Materials Program, Toronto, Ontario, M5G 1Z8, Canada.
Sci Rep. 2019 Jul 29;9(1):10974. doi: 10.1038/s41598-019-47517-6.
A recent inelastic neutron scattering experiment on the pyrochlore magnet YbTiO 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 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.
近期对烧绿石磁体YbTiO进行的非弹性中子散射实验发现，尽管基态存在展平的铁磁序，但自旋激发谱中仍出现了异常的散射连续体。在高磁场下存在明确的自旋波激发，然而随着磁场降低，单磁振子模式和双磁振子连续体开始强烈重叠，最终在零场时它们变成散射连续体。受这些观测结果的启发，我们在由之前两个实验确定交换参数的自旋模型中，研究具有分数化激发的磁有序基态的可能出现情况。使用费米子部分子平均场理论，我们表明在存在足够强的量子涨落时，具有分数化激发的磁有序态可以作为稳定的平均场基态出现。计算了这种基态下的自旋激发谱，并表明其具有散射连续体。随着磁场增加，分数化磁有序态受到抑制，最终在高场时被传统磁有序相取代，这与实验数据一致。我们讨论了这些结果对实验的进一步影响以及理论分析可能的改进。
