Linear dependence of peak width in χ(q, ω) vs Tc for YBa2Cu3O6+x superconductors

It is shown that the momentum space width of the peak in the spin susceptibility, Im chi(q,omega), is linearly proportional to the superconducting T-c: T-c = (h) over bar upsilon*Delta q with (h) over bar upsilon* similar or equal to 35 meV Angstrom. This relation is similar to the linear relation between incommensurate peak splitting and T-c in LaSrCuO superconductors, as first proposed by Yamada et al. [Phys. Rev. B 57, 6165 (1998)]. The velocity (h) over bar upsilon* is smaller than Fermi velocity or the spin-wave velocity of the parent compound and remains the same for a wide doping range. This result points towards strong similarities in magnetic state of YBa2Cu3O6+x and LaSrCuO.