Bilayer quantum Hall systems: spin-pseudospin symmetry breaking and quantum phase transitions

We discuss and review recent advances in our understanding of quantum Hall systems where additional quantum numbers associated with spin and/or layer (pseudospin) indices play crucial roles in creating exotic quantum phases. Among the novel quantum phases we discuss are the recently discovered cante d antiferromagnetic phase, the spontaneous interlayer coherent phase, and v arious spin Bose glass phases. We describe the theoretical models used in s tudying these novel phases and the various experimental techniques being us ed to search for these phases. Both zero temperature quantum phase transiti ons and finite temperature phase transitions are discussed. Emphasis in thi s article is on the recent developments in novel quantum phases and quantum phase transitions in bilayer quantum Hall systems where non-trivial magnet ic ground states associated with spontaneous spin symmetry breaking play ce ntral role. (C) 2001 Published by Elsevier Science Ltd.