U(1)XSU(2) GAUGE-THEORY OF UNDERDOPED CUPRATE SUPERCONDUCTORS

The U(1) x SU(2) Chern-Simons gauge theory is applied to study the 2D t-J model describing the normal state of underdoped cuprate supercondu ctors. The U(1) field produces a flux phase for holons converting them into Dirac-like fermions, while the SU(2) field, due to the coupling to holons gives rise to a gap for spinons. An effective low-energy act ion involving holons, spinons and a self-generated U(1) gauge field is derived. The Fermi surface and electron spectral function obtained ar e consistent with photoemission experiments. The theory predicts a min imal gap proportional to doping concentration. It also explains anomal ous transport properties.