Direct NMR evidence of phase solitons in the spin ground state of overdoped manganites.

Charge ordering phenomena in overdoped La 1-x Ca x MnO 3 (LCMO) manganites with x ≥ 0.5 are generally believed to be associated with the formation of charge stripes composed of alternating Mn 3+ and Mn 4+ charges. However, a number of recent experiments indicate that instead of stripes the charge in these systems is spatially organized in a uniform charge density wave. At the same time theory predicts that the ground state is modulated by an incommensurate (IC) orbital and charge soliton lattice. Here, by using nuclear magnetic resonance we provide the first direct evidence that the spin ground state in overdoped LCMO manganites is IC modulated with phase solitons. At higher temperatures the solitonic superstructure is replaced by a uniform spin-density wave, subjected to coherent slow fluctuations, showing a striking similarity with slow fluctuations in the striped phase of high T c cuprates and nickelates.