Two different types of pseudogaps in high-T_c superconductors

Ultrahigh-resolution (ΔE = 7 meV angle-resolved (ARPES) and angle-integrated (AIPES) photoemission spectroscopy have been performed on optimally doped Bi₂Sr₂CaCu₂O₈ (Bi2212) and La_1.85Sr_0.15CuO₄ (LSCO). The ARPES spectrum of Bi2212 at the (π, 0)-(π, π) crossing shows a pseudogap at E_F above T_c, which is smoothly connected from the superconducting gap across T_c and closes slightly above T_c (T* = 110 K). On the other hand, the AIPES spectra both in Bi2212 and LSCO show a remarkable depletion of the density of states in a relatively wider energy (100-150 meV) region near E_F. The temperature-induced filling of the depletion persists far above T_c and T*. This suggests that there are two different pseudogaps in the high-T_c superconductors; one is likely associated with pairing and the other is attributed to the development of antiferromagnetic correlation.