Superfluid properties of double-layer quantum Hall ferromagnets

Because of the degeneracy of 2D electron system Landau levels, quantum Hall systems exhibit a wide variety of non-trivial electron-electron interactio n effects. Double-layer systems with small layer separations have broken sy mmetry ground states that can be regarded either as easy-plane ferromagnets or as excitonic superfluids. In this contribution we discuss the superflui d properties of quantum Hall-ferromagnets. (C) 2001 Elsevier Science B.V. A ll rights reserved.