Nonlinear electron-phonon coupling in doped manganites

Dynamic of charge-order melting. (a) Transient response of a charge-order reflection for different fluences for pumping at λ=17  μm. b) Whereas excitation with near-IR pulses leads to a linear drop in diffraction intensity versus pump fluence the drop following mid-IR excitation is highly nonlinear.

The control of material properties using ultrashort pulses of light is a promising route for the development of future electro-optical storage and high speed switching devices. One very fruitful approach is to use low energy excitations in the mid-infrared spectral range to realize the targeted changes. The selectivity of the process minimizes the entropy added to the system as compared to the excitation of electronic transitions in the ultraviolet to near-infrared wavelengths range. In particular, the transient enhancement of superconductivity initiated via nonlinear phonon-phonon interactions is a nice example that has recently received large attention.

In this work, we report of a new route to manipulate the electronic properties of a material via vibrational excitation. Investigating the dynamics of the charge order in a manganites film following resonant excitation of a phonon mode to large amplitude, we find direct nonlinear coupling between the excited mode and the electronic degrees of freedom. In particular our work demonstrates that the nonlinear electron-phonon coupling is sufficiently strong to drive the insulator-metal transition in this material. The generalization of our approach leads to new ways of manipulating materials e.g. shaping their properties on ultrashort timescales.