YBA2CU3O7 - A NEARLY ANTIFERROMAGNETIC FERMI-LIQUID

We have carried out strong-coupling calculations using the Eliashberg formalism, which provide strong evidence for the description of the planar quasiparticles in YBa2Cu3O7 as a nearly antiferromagnetic Fermi liquid. We show that when one takes into account the full structure (in frequency and momentum space) of the spin-fluctuation-induced interaction between quasiparticles, a superconducting transition temperature of 90 K is obtained with a dimensionless coupling constant, lambda=0.402N(0)g=0.83, for a hole concentration of 0.25, a quasiparticle spectrum characterized by nearest-neighbor hopping, t=0.25 eV, and a spin-fluctuation spectrum determined by experiment. With a next-nearest-neighbor hopping, t'=-0.45t, the coupling required to obtain a T(c) of 90 K is reduced by some 10%. Strong-coupling calculations of the normal state, using these latter parameters, yield a resistivity that varies linearly with temperature, with a magnitude at 90 K of 62 muOMEGA cm, a frequency dependence of the optical conductivity in quantitative agreement with experiment for energies less-than-or-equal-to 0.1 eV, a quasiparticle spectrum characterized by a momentum-dependent wave-function renormalization constant, 0.4 less-than-or-equal-to Z(p) less-than-or-equal-to 0.6, and a self-energy whose imaginary part is proportional to omega for energies up to 0.25 eV. We give a progress report on the extent to which a self-consistent description of the spin-fluctuation excitation spectrum can be found by taking chi(q,omega)=chi(q,omega)/[1-J(q)chi(q,omega)], where chi(q,omega) is the irreducible particle-hole susceptibility calculated for quasiparticles coupled to spin excitations whose spectrum is given by chi(q,omega) and J(q) is the effective spin-spin coupling.