Effect of Normal-State Pseudogap on Physical Quantities in Hubbard Model for Underdoped High-T_c Cuprates

摘要

We develop the strong-coupling theory of coexisting charge-density-wave (CDW) and superconductivity d-wave gaps within the framework of the FLEX (fluctuation exchange) approximation for the two-dimensional Hubbard model. For nested sections of the Fermi surface these equations reduce to the previous FLEX equations for superconductivity where the squared energy gap φ_s~2 in the denominator of the Green's function is replaced by (φ_s~2 ＋ φ_c~2) (here φ_s is the superconductivity and φ_c the CDW gap). We solve these equations by taking for φ_c a phenomenological d-wave gap. The resulting neutron scattering intensity, spin-lattice relaxation rate 1/T_1, Knight shift, resistivity, and photoemission intensity are in qualitative agreement with the data on underdoped high-T_c cuprates. The T_c for superconductivity decreases and the crossover temperature T_* for 1/T_1T increases with increasing gap amplitude of φ_c which is in qualitative agreement with the phase diagram for underdoped cuprates.