Weak ferromagnetism and excitonic condensates

We investigate a model of excitonic ordering (i.e., electron-hole pair condensation) appropriate for divalent hexaborides. We show that the inclusion of imperfectly nested electron-hole Fermi surfaces can lead to the formation or an undoped excitonic metal phase. In addition, we find that weak ferromagnetism with compensated moments arises as a result of gapless excitations. We study the effect of low-lying excitations on the density of states, Fermi-surface topology, and optical conductivity, and compare to available experimental data.