Excitation gaps in the orbitally degenerate Hubbard model

Abstract

The excitation gaps for the two-orbital degenerate Hubbard model are investigated byapplying a generalized version of Lieb’s spin-reflection positivity. Combining the knownexact results on the ground state, and making use of symmetry properties, we rigorouslyshow that, at half-filling, the charge gaps are always larger than the spin-excitation gapsand properly defined orbital gaps.