Ultrafast spin-nematic and ferroelectric phase transitions in a photo-induced charge and orbital ordered manganite

Manganites are a class of materials in which charge, spin, and lattice degrees are strongly coupled and known to actively participate in the energy conversion processes. Experimental studies of optical manipulation of spin orders in manganites show these systems are promising materials for the opto-spintronics. However, the intrinsic mechanisms governing the photo-induced magnetic phase transitions are not very well understood and require microscopic knowledge of the energy conversion processes. The time and length scales of the phonon and spin dynamics in such systems are beyond the scope of the traditional first-principles approaches, such as TD-DFT. Combining a tight-binding model with Ehrenfest dynamics, we studied the photo-excitation and the subsequent non-equilibrium dynamics in charge- and orbital-ordered manganites. We propose a mechanism for the optical excitation of a non-collinear antiferromagnet leading selectively to new spin orders beyond a critical light-intensity. The optical excitations produce two distinct and highly interesting novel phases; a spin-nematic and a ferroelectric phase. A specific phase is selected by the polarization of the light pulse.