Observation of nonconventional spin waves in composite-fermion ferromagnets |
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Authors: | Wurstbauer U Majumder D Mandal S S Dujovne I Rhone T D Dennis B S Rigosi A F Jain J K Pinczuk A West K W Pfeiffer L N |
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Affiliation: | Department of Physics, Columbia University, New York, New York 10027, USA. uw2106@columbia.edu |
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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. |
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