Evolution of the Fermi surface with carrier concentration in Bi_2Sr_2CaCu_2O_{8+δ}

Abstract

We show, by use of angle-resolved photoemission spectroscopy, that underdoped Bi_2Sr_2CaCu_2O_{8+δ} appears to have a large Fermi surface centered at (π,π), even for samples with a T_c as low as 15 K. No clear evidence of a Fermi surface pocket around (π/2,π/2) has been found. These conclusions are based on a determination of the minimum gap locus in the pseudogap regime T_c < T < T^*, which is found to coincide with the locus of gapless excitations in momentum space (Fermi surface) determined above T^*. These results suggest that the pseudogap is more likely of precursor pairing rather than magnetic origin.