Abstract
Graphene exhibits quantum Hall ferromagnetism in which an approximate symmetry involving spin and valley degrees of freedom is spontaneously broken. We construct a set of integer and fractional quantum Hall states that break the spin (valley) symmetry, and study their neutral and charged excitations. Several properties of these ferromagnets can be evaluated analytically in the symmetric limit, including the full collective-mode spectrum at integer fillings. By constructing explicit wave functions we show that the lowest-energy skyrmion states carry charge for any integer filling, and that skyrmions are the lowest-energy-charged excitations for graphene Landau-level index . We also show that the skyrmion lattice states which occur near integer-filling factors support four gapless collective-mode branches in the presence of full symmetry. Comparisons are made with the more familiar quantum Hall ferromagnets studied previously.
- Received 30 May 2006
DOI:https://doi.org/10.1103/PhysRevB.74.075423
©2006 American Physical Society