非局域非线性声子学
Nonlocal nonlinear phononics
摘要：
非线性声子学依赖于红外活性晶格振动的共振光激发，以相干地诱导固体中的目标结构变形。这种形式的动态晶体结构设计已被应用于控制许多有趣系统的功能特性，包括磁阻锰氧化物，磁性材料，超导体和铁电体。然而，到目前为止，声子已被限制在协议中，结构变形发生局部内的光激发体积，有时会导致不必要的加热。在这里，我们扩展非线性声子传播极化激元，有效地分离在空间中的光学驱动器的功能响应。中红外光脉冲被用来共振驱动18太赫兹声子在铁电铌酸锂表面。时间分辨的受激拉曼散射探针揭示了铁电极化在样品的整个50微米深度上降低，远远超出了渐逝声子场的~微米深度。我们属性的铁电极化体响应的激发传播的2.5太赫兹软模声子极化激元。对于最高的激发振幅，我们达到了一个制度，其中的极化是逆转的。在这个非微扰制度，我们预计，极化激元模型演变成一个孤立的域壁，从表面传播到材料在接近光速。
英文摘要：
Nonlinear phononics relies on the resonant optical excitation of infrared-active lattice vibrations to coherently induce targeted structural deformations in solids. This form of dynamical crystal-structure design has been applied to control the functional properties of many interesting systems, including magneto-resistive manganites, magnetic materials, superconductors, and ferroelectrics. However, phononics has so far been restricted to protocols in which structural deformations occur locally within the optically excited volume, sometimes resulting in unwanted heating. Here, we extend nonlinear phononics to propagating polaritons, effectively separating in space the optical drive from the functional response. Mid-infrared optical pulses are used to resonantly drive an 18 THz phonon at the surface of ferroelectric LiNbO3. A time-resolved stimulated Raman scattering probe reveals that the ferroelectric polarization is reduced over the entire 50 micron depth of the sample, far beyond the ~ micron depth of the evanescent phonon field. We attribute the bulk response of the ferroelectric polarization to the excitation of a propagating 2.5 THz soft-mode phonon-polariton. For the highest excitation amplitudes, we reach a regime in which the polarization is reversed. In this this non-perturbative regime, we expect that the polariton model evolves into that of a solitonic domain wall that propagates from the surface into the materials at near the speed of light.
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