First time determination of the microscopic structure of a stripe phase: low temperature NMR in La(2)NiO(4.17).

The experimental observations of stripes in superconducting cuprates and insulating nickelates clearly show the modulation in charge and spin density. However, these have proven to be rather insensitive to the harmonic structure and (site or bond) ordering. Using (139)La NMR in La(2)NiO(4+delta) with delta = 0.17, we show that in the 1/3 hole doped nickelate below the freezing temperature the stripes are strongly solitonic and site ordered with Ni(3+) ions carrying S = 1/2 in the domain walls and Ni(2+) ions with S = 1 in the domains.