Potential of the AFD R-point mode at equilibrium (grey, negative time delay), with the corresponding variance in its amplitude indicated as the red-shaded area. At zero time delay, the potential softens due to coupling to the resonantly driven infrared-active phonon mode, enhancing the fluctuations <u_AFD^2> . At positive time delays, the onset of strain hardens the potential, reducing <u_AFD^2> fluctuations to below their equilibrium value.
