Lawrence Berkeley National Laboratory

This short paper summarizes the results we presented at the LEHTSC2007 conference. Recent doping and temperature dependence of angle-resolved photoemission data of underdoped superconducting cuprate Bi2Sr2CaCu2O8 (Bi2212) have revealed the presence of two energy scales exhibiting distinct behaviours [1,2]. One, which dominates the antinodal region, increases with underdoping and does not show obvious temperature dependence across Tc. This is a behaviour known for more than a decade and considered as the general gap behaviour in the underdoped regime. The other, which dominates the near-nodal regime, does not increase with less doping and opens near Tc via a BCS-like temperature dependence. This is a behaviour not previously observed in the single particle spectra. We propose a momentum space picture of these two energy scales or energy gaps that could resolve the seemingly contradictory gap measurements among different experimental techniques. Our results have also further constrained the theory for high-Tc superconducting cuprates.