Physics – Condensed Matter – Mesoscale and Nanoscale Physics
Scientific paper
2006-05-26
Phys. Rev. B 74, 075423 (2006)
Physics
Condensed Matter
Mesoscale and Nanoscale Physics
Added references. Final version as appeared in print
Scientific paper
10.1103/PhysRevB.74.075423
Graphene exhibits quantum Hall ferromagnetism in which an approximate SU(4) 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 SU(4) spin/valley symmetry, and study their neutral and charged excitations. Several properties of these ferromagnets can be evaluated analytically in the SU(4) 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 $\pm 1$ for {\em any} integer filling, and that skyrmions are the lowest energy charged excitations for graphene Landau level index $|n| \le 3$. 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 SU(4) symmetry. Comparisons are made with the more familiar SU(2) quantum Hall ferromagnets studied previously.
MacDonald Allan. H.
Sarma Sankar Das
Yang Kun
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