Neutral Fermions at Filling Factorν=1/2

Abstract

We present a particle-hole symmetric theory for a two-dimensional electron gas at filling factor $\ensuremath{\nu}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1/2$. In this theory, elementary excitations are dipolelike fermions floating on top of the $\ensuremath{\nu}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1/2$ boson quantum-Hall liquid. In the absence of disorder these dipoles can form a Fermi liquid. Disorder can break them apart and drive the ground state into a quantum critical state.