Small and large pseudogaps in high-T-c superconductors observed by ultrahigh-resolution photoemission spectroscopy

Two different (small and large) pseudogaps have been observed by ultrahigh- resolution photoemission spectroscopy in optimally doped Bi2Sr2CaCu2O8 and La1.85Sr0.15CuO4. The small pseudogap is smoothly connected from the superc onducting gap and closes slightly above T-c, while the large one appears as a remarkable depletion of the density of states in a wider energy range ne ar E-F and persists far above T-c. The small pseudogap is likely associated with pairing and the large one is ascribed to the development of antiferro magnetic correlation.