Liquid-crystal phases of quantum Hall systems

Mean-field calculations for the two-dimensional electron gas in a large magnetic field with a partially filled Landau level with index $N>~2$ consistently yield ``stripe-ordered'' charge-density wave ground states, for much the same reason that frustrated phase separation leads to stripe-ordered states in doped Mott insulators. We have studied the effects of quantum and thermal fluctuations about such a state and show that they can lead to a set of electronic liquid crystalline states, particularly a stripe-nematic phase, which is stable at $T>0.$ Recent measurements of the longitudinal resistivity of a set of quantum Hall devices have revealed that these systems spontaneously develop, at low temperatures, a very large anisotropy. We interpret these experiments as evidence for a stripe nematic phase, and propose a general phase diagram for this system.