Spin-flip excitations in bilayer quantum Hall ferromagnets

Bilayer quantum Hall systems at v = 1 are believed to have a ground state with spontaneous spin-polarization and spontaneous interlayer phase coherence. In this paper, we address the spectrum of spin-flip collective excitations using a generalized lattice spin model that appeals to the quantum Hall gap to justify neglect of charge fluctuations. We find that the long wavelength spin-flip excitation spectrum consists of the global Larmor spin-wave mode and a higher energy mode in which spin-waves in the two-layers are out of phase. We address the dependence of the energy splitting of the two modes on quantum fluctuations in the bilayer ground state. (C) 2005 Published by Elsevier Ltd.