Nonlocal Nonlinear Phononics

Nonlinear phononics in solids involves the resonant optical excitation of infrared-active lattice vibrations to a regime in which they can drive other modes through anharmonic coupling. This unique form of selective lattice control has led to the ultrafast manipulation of superconductivity, magnetism, and ferroelectricity in complex materials. However, studies in nonlinear phononics have thus far focused on the response of the material within the few-micron depth of the optically excited volume. In my talk, I will show that functional control through nonlinear phononics extends to polarization waves which propagate well-beyond the excited region. In our experiments, mid-infrared optical pulses were used to resonantly excite an 18 THz phonon below the surface of ferroelectric LiNbO3. A time-resolved stimulated Raman scattering probe revealed that the ferroelectric polarization was manipulated over the entire 50 μm depth of the sample, far beyond the few μm depth of the optically-driven phonon. At the highest excitation fluence, we observed a transient reversal of the ferroelectric polarization. These results build upon a paradigm for nonlocal material control in which the functional response of a material is altered in a region that is untraversed by the optical driving field.