V-51-NMR studies on the spin dynamics of S=1/2 zig-zag chains of VO5 pyramids

NMR Knight shifts K and nuclear relaxation rates 1/T-1 have been studied on the V4+ sites of two compounds [N(CH3)(4)]V3O7 and (en)(2)ZnV6O14 which ar e known to exhibit spin-gap behavior from their susceptibility data. The ac tivation-type behavior has been observed in K and 1/T-1, confirming the exi stence of the spin-gap in these systems. The frequency (omega(N)) dependenc e of 1/T-1 of [N(CH3)(4)]V3O7 has been found to he 1/root omega(N)-type one and 1/T-1 of (en)(2)ZnV6O14 is linear in -ln(omega(N)), indicating the dif fusive and ballistic characters of the triplet excitations, respectively. T he results are discussed in relation to the theory recently developed by Sa chdev and Damle [Phys. Rev. B 57 (1998) 8307].