  We suggest that the 2+1 dimensional Gross-Neveu model can give an effective
field theory description of low-energy quasiparticles in high temperature
superconductors. The magnetic catalysis of dynamical symmetry breaking is
examined. The model shows that a magnetic field can induce a phase transition
associated with parity breaking. In particular, it is intended to give an
explanation of a second phase transition observed in a recent experiment by
Krishana et al.
