Solitonic Phase in Manganites

Whenever a symmetry in the ground state of a system is broken, topological defects will exist. These defects are essential for understanding phase transitions in low dimensional systems[1]. Excitingly in some unique condensed matter systems the defects are also the low energy electric charge excitations. This is the case of skyrmions in quantum Hall ferromagnets[2] and solitons in polymers[3]. Orbital order present in several transitions metal compounds[4-6] could give rise to topological defects. Here we argue that the topological defects in orbital ordered half doped manganites are orbital solitons. Surprisingly, these solitons carry a fractional charge of $\pm$e/2, and whenever extra charge is added to the system an array of solitons is formed and an incommensurate solitonic phase occurs. The striking experimental asymmetry in the phase diagram as electrons or holes are added to half doped manganites[7-12], is explained by the energy difference between positive and negative charged solitons. Contrary to existent models that explain coexistence between phases in manganites as an extrinsic effect[13-14], the presence of inhomogeneities is naturally explained by the existence of solitonic phases. The occurrence and relevance of orbital solitons might be a general phenomena in strongly correlated systems.