Reconstructed Fermi Surface of Underdoped Bi2Sr2CaCu2O8+δ Cuprate Superconductors

The Fermi surface topologies of underdoped samples of the high-Tc superconductor Bi2Sr2CaCu2O8+delta have been measured with angle resolved photoemission. By examining thermally excited states above the Fermi level, we show that the observed Fermi surfaces in the pseudogap phase are actually components of fully enclosed hole pockets. The spectral weight of these pockets is vanishingly small at the magnetic zone boundary, creating the illusion of Fermi arcs. The area of the pockets as measured in this study is consistent with the doping level, and hence carrier density, of the samples measured. Furthermore, the shape and area of the pockets is well reproduced by phenomenological models of the pseudogap phase as a spin liquid.