Spin Gaps and Spin Dynamics in Superconducting Cuprates

Spin gap effects, consisting of a declining uniform susceptibility and spin paramagnetic NMR shift at low temperatures in the normal state and associated T(1) behavior, are discussed and documented in several cuprate superconductors. Dynamic spin magnetism in these systems is further reviewed in the light of mean-field models, where we note that detailed results from the model by Millis, Monien, and Pines are not borne out in recent neutron data on YBa(2)Cu(3)O(6.92). T(1) data on (17)O in La(1.85)Sr(0.15)CuO(4) are presented, showing consistency with neutron dynamic susceptibility data for T >= 80 K, but exhibiting a strong spin gap character below 80 K which is not present in the neutron data. Data for Zn-doped YBCO with T(c) approximate to 60 K are also presented, showing strong RKKY broadening from localized moments in the planes, but no spin gap effect such as that found in the T(c) = 60 K oxygen-deficient phase.