  The spin dynamics of an optimally doped YBa2Cu3O7 (Tc = 93 K) crystal array
have been investigated in a wide range of momentum and energy (Q - E) space
using the time-of-flight neutron scattering method. Incommensurate spin
modulation in Q is a characteristic feature, as it is in the under-doped
YBa2Cu3O6.7 with a different incommensurability. A linear relationship between
the incommensurability and Tc is proposed. Along with the discovery of the same
incommensurability in under-doped La2-ySryCuO4, it may be a generic
characteristic of the high-Tc oxide superconductor.
