title: Observation of nonconventional spin waves in composite-fermion ferromagnets.
abstract: 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.
authors: Department of Physics, Columbia University, New York, New York 10027, USA. uw2106@columbia.edu
authors: U
authors: U
authors: Wurstbauer
authors: D
authors: D
authors: Majumder
authors: S S
authors: SS
authors: Mandal
authors: I
authors: I
authors: Dujovne
authors: T D
authors: TD
authors: Rhone
authors: B S
authors: BS
authors: Dennis
authors: A F
authors: AF
authors: Rigosi
authors: J K
authors: JK
authors: Jain
authors: A
authors: A
authors: Pinczuk
authors: K W
authors: KW
authors: West
authors: L N
authors: LN
authors: Pfeiffer