Two different types of pseudogaps in high-T-c superconductors

Ultrahigh-resolution (DeltaE = 7 meV angle-resolved (ARPES) and angle-integ rated (AIPES) photoemission spectroscopy have been performed on optimally d oped Bi2Sr2CaCu2O8 (Bi2212) and La1.85Sr0.15CuO4 (LSCO). The ARPES spectrum of Bi2212 at the (pi, 0)-(pi, pi) crossing shows a pseudogap at EF 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 spect ra both in Bi2212 and LSCO show a remarkable depletion of the density of st ates in a relatively wider energy (100-150 meV) region near EF The temperat ure-induced filling of the depletion persists far above T-c and T-*. This s uggests that there are two different pseudogaps in the high-T-c superconduc tors: one is likely associated with pairing and the other is attributed to the development of antiferromagnetic correlation. (C) 2000 Elsevier Science Ltd. All rights reserved.