Excitation spectrum of bilayer ν=2 quantum Hall systems

Excitation spectra in bilayer quantum Hall systems at total Landau-level filling ν=2 are studied by the Hartree–Fock–Bogoliubov approximation. The systems have the spin degrees of freedom in addition to the layer degrees of freedom described in terms of pseudospin. On the excitation spectra from spin-unpolarized and pseudospin-polarized ground state, this approximation fully preserves the spin rotational symmetry and thus can give not only spin-triplet but also spin-singlet excitations systematically. It is also found that the ground-state properties are well described by this approximation.