揭示量子霍尔铁磁体中磁振子的激子性质
Unveiling excitonic properties of magnons in a quantum Hall ferromagnet
摘要：
磁振子能够在宏观距离上传递磁矩或自旋。在量子霍尔铁磁体中，人们在90年代早期预测自旋和电荷是纠缠的，这意味着自旋纹理的任何变化都会改变电荷分布。作为这种纠缠的直接结果，磁振子携带电偶极矩。在这里，我们报告的第一个证据存在的石墨烯量子霍尔铁磁体使用马赫-曾德尔干涉仪作为量子传感器的电偶极矩。磁振子电偶极矩通过绝缘体向干涉仪传播，改变了通过干涉仪的Aharonov-Bohm通量，改变了其相位和可见度。特别是，我们与相移的符号，这个电偶极矩，和指数损失的可见性的通量发射的磁振子。最后，我们探讨了接近填充因子v=1的磁振子的发射能量阈值。接近v=0时，我们观察到发射能量阈值向零减小，这可能与v=0时斜反铁磁（CAF）相中无带隙模式的存在有关。基于磁振子电偶极子的磁振子的探测和操纵，为静电控制的新型相干磁振子量子线路开辟了领域。
英文摘要：
Magnons enable transferring a magnetic moment or spin over macroscopic distance. In quantum Hall ferromagnet, it has been predicted in the early 90s that spin and charges are entangled, meaning that any change of the spin texture modifies the charge distribution. As a direct consequence of this entanglement, magnons carry an electric dipole moment. Here we report the first evidence of the existence of this electric dipole moment in a graphene quantum Hall ferromagnet using a Mach-Zehnder interferometer as a quantum sensor. By propagating towards the interferometer through an insulating bulk, the magnon electric dipole moment modifies the Aharonov-Bohm flux through the interferometer, changing both its phase and its visibility. In particular, we relate the phase shift to the sign of this electric dipole moment, and the exponential loss of visibility to the flux of emitted magnons. Finally, we probe the emission energy threshold of the magnons close to filling factor v=1. Approaching v=0, we observe that the emission energy threshold diminishes towards zero, which might be linked to the existence of gapless mode in the canted-antiferromagnetic (CAF) phase at v=0. The detection and manipulation of magnons based on their electric dipole open the field for a new type of coherent magnon quantum circuits that will be electrostatically controlled.
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