Meta—stability and Transient Phases Triggered by Optically Excited Quasi--particles in Strongly Correlated Systems.*

The interplay between electronic, magnetic and lattice degrees of freedom in colossal magnetoresistant manganites results in a rich phase diagram that provides an ideal model system for phase transition studies. Here we investigate the possibility of phase transitions induced by ultrafast optical laser pulses. We use a generalized tight—binding model, based on Hubbard operators, to describe the interaction between itinerant carrier and localized magnetic moment in multi--electron configurations. Optically—induced quasi—particle excitations introduce inhomogeneities, charge redistributions and spin fluctuations resulting in the formation of meta—stable states that trigger a non-equilibrium ultrafast dynamics. We discuss a theoretical description of optical switching mechanism between coexisting phases and highlight the role of photo—induced non—linearities on quantum femptosecond magnetism.