The Fermi surface of underdoped high-Tc superconducting cuprates

The coexistence of π-flux state and d-wave RVB state is considered in this paper within the slave boson approach. A critical value of doping concentration δc is found, below which the coexisting π-flux and d-wave RVB state is favored in energy. The pseudo Fermi surface of spinons and the physical electron spectral function are calculated. A clear Fermi-level crossing is found along the (0,0) to (π, π) direction, but no such crossing is detected along the (π, 0) to (π, π) direction. Also, an energy gap of d-wave symmetry appears at the Fermi level in our calculation. The above results are in agreement with the angle-resolved photoemission experiments which indicate at a d-wave pseudo-gap and a half-pocket-like Fermi surface in underdoped cuprates. PACS Numbers: 71.27.+a, 71.10.Pm, 71.10.Hf Typeset using REVTEX 1