Distinct charge and spin gaps in underdoped YBa2Cu3O7-δ from analysis of NMR, neutron scattering, tunneling, and quasiparticle relaxation experiments

A systematic quantitative comparison of "pseudogap" values obtained from the analysis of charge and spin excitation spectroscopies in underdoped YBa2Cu3O7-delta using a temperature-independent gap shows two distinct excitations, one visible in spin-flip spectroscopies like NMR and spin-polarized neutron scattering, and the other in charge excitation spectroscopies like single-particle tunneling and time-resolved quasiparticle relaxation. Both appear to decrease with doping x approximately as 1/x and are T independent, existing above and below T-c. We suggest that the charge excitation can be attributed to a pair-breaking local gap, while the spin excitation can be explained by an intragap local triplet-state. [S0163-1829(99)50634-6].