Fermi Surface Topology and Energy Gap of Heavily Underdoped Bi2212 Studied by Laser ARPES*

The high temperature cuprate superconductors exhibit a number of exotic properties especially in the underdoped region. Here we have carried out high resolution angle-resolved photoemission (ARPES) measurements on heavily underdoped Bi2Sr2CaCuO8 (Bi2212) superconductors by using our new laser-based ARPES system equipped with angle-resolved time-of-flight analyzer and 7 eV and 11 eV laser sources. We have synthesized high quality heavily underdoped Bi2212 single crystals with different dopings by Dy substitution of calcium and vacuum annealing. Taking advantage of our high resolution laser-ARPES, we have systematically studied the Fermi surface topology, the energy gap and the many-body effects in these heavily underdoped Bi2212. Implications of these results will be discussed.