Evolution of the Magnetic and Polaronic Order of Pr_1/2Ca_1/2MnO_3 Following an Ultrashort Light Pulse

The dynamics of electrons, spins and phonons induced by optical femtosecond pulses has been simulated for the polaronic crystal Pr_1/2Ca_1/2MnO_3. The model used for the simulation has been derived from first-principles calculations. The simulations reproduce the experimentally observed melting of charge/orbital order with increasing fluence. The loss of charge order in the high-fluence regime induces a transition to a ferromagnetic metal. At low fluence, the dynamics is deterministic and coherent phonons are created by the repopulation of electronic orbitals, which are strongly coupled to the phonon degrees of freedom. In contrast to the low-fluence regime, the magnetic transitions occurring at higher fluence can be attributed to a quasi-thermal transition of a cold-plasma-like state with hot electrons and cold phonons and spins. The findings can be rationalized in a more complete picture of the electronic structure that goes beyond the simple ionic picture of charge order.