Systematic 63Cu NQR study of the stripe phase in La1.6-xNd0.4SrxCuO4 for 0.07<~x<~0.25

We demonstrate that the integrated intensity of 63Cu nuclear quadrupole resonance (NQR) in La1.6-xNd0.4SrxCuO4 decreases dramatically below the charge-stripe ordering temperature Tcharge. Comparison with neutron and x-ray scattering indicates that the wipeout fraction F(T) (i.e., the missing fraction of the integrated intensity of the NQR signal) represents the charge-stripe order parameter. The systematic study reveals bulk charge-stripe order throughout the superconducting region 0.07<~x<~0.25. As a function of the reduced temperature t≡T/Tcharge, the temperature dependence of F(t) is sharpest for the hole concentration x∼1/8, indicating that x∼1/8 is the optimum concentration for stripe formation.