Excitonic nature of magnons in a quantum Hall ferromagnet
Excitonic nature of magnons in a quantum Hall ferromagnet
复制标题
量子霍尔铁磁体中磁振子的激子性质
作者：
A. Assouline;M. Jo;P. Brasseur;K. Watanabe;T. Taniguchi;T. Jolicoeur;D. Glattli;N. Kumada;P. Roche;F. Parmentier;P. Roulleau
磁振子能够在宏观距离上传输磁矩或自旋。在量子霍尔铁磁体中，人们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，磁振子应该带有电偶极矩。在这里，我们使用马赫-曾德尔干涉仪报告了石墨烯量子霍尔铁磁体 2,3 中电偶极矩的证据。当磁振子在绝缘体上传播时，它们的电偶极矩会改变通过干涉仪的阿哈罗诺夫-玻姆通量，从而影响干涉图样的相位和可见性。特别是，我们将相移与电偶极矩的符号以及发射磁振子通量的可见性损失联系起来，并且我们证明磁振子发射是泊松过程。最后，我们探讨了瞬态磁振子的发射能量阈值，介于 ν = 0 和 ν = 1 之间，并将它们与电荷中性时倾斜反铁磁相中预测的无间隙模式的出现联系起来4,5。将自旋自由度与静电势耦合的能力是量子霍尔铁磁体的一种特性，这对于自旋电子学来说可能是有希望的。被称为磁振子的传播自旋波预计在量子霍尔体系中携带偶极矩。现在，这个时刻已经被检测到，证明自旋和电荷的自由度与量子霍尔磁振子纠缠在一起。
Magnons enable the transfer of a magnetic moment or spin over macroscopic distances. In quantum Hall ferromagnets, it has been predicted1 that spin and charge are entangled, meaning that any change in the spin texture modifies the charge distribution. As a direct consequence of this entanglement, magnons should carry an electric dipole moment. Here we report evidence of this electric dipole moment in a graphene quantum Hall ferromagnet2,3 using a Mach–Zehnder interferometer. As magnons propagate across the insulating bulk, their electric dipole moment modifies the Aharonov–Bohm flux through the interferometer, affecting both phase and visibility of the interference pattern. In particular, we relate the phase shift to the sign of this electric dipole moment and the loss of visibility to the flux of emitted magnons, and we show that the magnon emission is a Poissonian process. Finally, we probe the emission energy threshold of the magnons for transient states, between ν = 0 and ν = 1, and link them to the emergence of the gapless mode predicted in the canted-antiferromagnetic phase at charge neutrality4,5. The ability to couple the spin degree of freedom to an electrostatic potential is a property of quantum Hall ferromagnets that could be promising for spintronics. Propagating spin waves known as magnons are expected to carry a dipole moment in the quantum Hall regime. Now, this moment has been detected, demonstrating that the degrees of freedom of spin and charge are entangled in quantum Hall magnons.