Department of Physics, Columbia University, New York, New York 10027, USA.
Phys Rev Lett. 2011 Aug 5;107(6):066804. doi: 10.1103/PhysRevLett.107.066804. Epub 2011 Aug 2.
We find unexpected low energy excitations of fully spin-polarized composite-fermion ferromagnets in the fractional quantum Hall liquid, resulting from a complex interplay between a topological order manifesting through new energy levels and a magnetic order due to spin polarization. The lowest energy modes, which involve spin reversal, are remarkable in displaying unconventional negative dispersion at small momenta followed by a deep roton minimum at larger momenta. This behavior results from a nontrivial mixing of spin-wave and spin-flip modes creating a spin-flip excitonic state of composite-fermion particle-hole pairs. The striking properties of spin-flip excitons imply highly tunable mode couplings that enable fine control of topological states of itinerant two-dimensional ferromagnets.
我们在分数量子霍尔液体中发现了完全自旋极化复合费米子铁磁体出人意料的低能激发，这是由于拓扑有序通过新能级和由于自旋极化引起的磁有序之间的复杂相互作用。涉及自旋反转的最低能量模式在小动量下表现出非传统的负色散，然后在较大动量下出现深罗顿最小值，这是非常显著的。这种行为是由于自旋波和自旋翻转模式的复杂混合，从而产生了复合费米子粒子-空穴对的自旋翻转激子态。自旋翻转激子的显著性质意味着可以高度调整模式耦合，从而能够精细控制巡游二维铁磁体的拓扑状态。
