Cu-63 NQR evidence of dimensional crossover to anisotropic 2D regime in S = (1)/(2) three-leg ladder Sr2Cu3O5

We probed spin-spin correlations up to 725 K with Cu-63 nuclear quadrupole resonance in the S = 1/2 three-leg ladder Sr2Cu3O5. We present experimental evidence that below 300 K weak interladder coupling causes dimensional cro ssover of the spin-spin correlation length xi from the quasi-1D (xi similar to 1/T) to the anisotropic 2D regime (xi similar to exp (2 pi rho s)/(T), where 2 pi rho(s) = 290 +/- 30 K is the effective spin stiffness). PACS num bers: 74.72.Jt, 74.25.Nf, 76.60.-k.