Particle-hole symmetry and the Dirac composite fermion*

Composite fermion is a central notion in quantum Hall physics. For a long time, field theories of the composite fermion suffers from the lack of particle-hole symmetry, an exact symmetry of the lowest Landau level. I will describe how recent theoretical ideas have lead to a new understanding of the physics of the half-filled Landau level. According to the new picture, the composite fermion at half filling is a Dirac particle with a nontrivial pi Berry phase around the Fermi surface. Consequences of the new proposal are outlined.