Photo-modulated dynamic competition between metallic and insulating phases in a layered manganite

We show evidence that the competition between the antiferromagnetic metallic phase and the charge- and orbital-ordered insulating phase at the reentrant phase boundary of a layered manganite, LaSr₂Mn ₂O₇, can be manipulated using ultrafast optical excitation. The time-dependent evolution of the Jahn-Teller superlattice reflection, the indicator of the formation of charge and orbital order, was measured at different laser fluences. The laser-induced change in the Jahn-Teller reflection intensity shows a reversal of sign between earlier (∼10 ns) and later (∼150 ns) times during the relaxation of the sample. This is consistent with a physics picture whereby the laser excitation modulates the local competition between the metallic and the insulating phases.