Cooper pair and spin fluctuations in underdoped high-temperature superconductors

We have calculated the quasiparticle self-energy Sigma (k,omega), spectral function N(k,omega), and density of states N(omega) due to exchange of spin and d-wave pair fluctuations above T-c in the FLEX (fluctuation exchange) approximation. We find that for T --> T-c a pseudogap evolves in N(omega) which is similar to the structure caused by the superconducting d-wave gap below T-c. A satellite peak occurs in N(k,omega) for k near (pi, 0) which is caused by a peak in -Im Sigma (k,omega). Since these effects become relatively weak at higher temperatures T similar or equal to 2T(c), however, we have to conclude that fluctuations of the pair amplitude within this spin fluctuation pairing scenario cannot explain the observed pseudogap behavior well above T-c in underdoped cuprates.