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The origin of the effect of colossal magneto-resistance (CMR) remains stillunexplained. In this work we revisit the spin dynamics of the pseudo-cubicLa1-xSrxMnO3 along the Mn-O-Mn bond direction at four x doping values (x < 0.5)and various temperatures and report a new lattice dynamics study at x0=0.2,representative of the optimal doping for CMR. We propose an interpretation ofthe spin dynamics in terms of orbital polarons. This picture is supported bythe observation of a discrete magnetic energy spectrum Enmag (q) characteristicof the internal excitations of "orbital polarons" defined by Mn3+ neighborssurrounding a Mn4+ center with a hole. Because of its hopping, the hole mixesup dynamically all the possible orbital configurations of its surrounding Mn3+sites with degenerate energies. The Enmag values indicate a lift of orbitaldegeneracy by phonon excitations. The number n varies with the spatialdimension D of the polaron and the q-range determines its size. At x=0.125 andx=0.3 the spectrum reveals 2D polarons coupled by exchange and 3D "free"polarons respectively, with sizes l=1.67a < 2a in all bond directions. Atx0=0.2, the spin and the lattice dynamics provide evidence for chains oforbital polarons of size l=2a with a periodic distribution over ~ 3a and aninteraction energy ~ 3 meV. At T < Tc the charges propagate together with thelongitudinal acoustic phonons along the chains enhancing their ferromagneticcharacter. The phase separation between metallic and ferromagnetic chains in anon-metallic matrix may be crucial for CMR.

Interacting chains of orbital polarons in "Colossal" magnetoresistive La1-xSrxMnO3 revealed by spin and lattice dynamics