The control of acoustic phonons, which are the carriers of sound and heat, has become the focus of increasing attention because of a demand for manipulating the sonic and thermal properties of nanometric devices. In particular, the photoacoustic effect using ultrafast optical pulses has a promising potential for the optical manipulation of phonons in the picosecond time regime. So far, its mechanism has been mostly based on the commonplace thermoelastic expansion in isotropic media, which has limited applicability. In this study, we investigate a conceptually new mechanism of the photoacoustic effect involving a structural instability that utilizes a transition-metal dichalcogenide VTe₂ with a ribbon-type charge-density-wave (CDW). Ultrafast electron microscope imaging and diffraction measurements reveal the generation and propagation of unusual acoustic waves in a nanometric thin plate associated with optically induced instantaneous CDW dissolution. Our results highlight the capability of photoinduced structural instabilities as a source of coherent acoustic waves.

中文翻译：

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薄片VTe2中异常光声波的纳米级成像。

由于需要操纵纳米器件的声波和热学性质，控制声子作为声和热的载体已成为人们越来越关注的焦点。特别地，使用超快光脉冲的光声效应具有在皮秒时间范围内对声子进行光学操纵的潜在潜力。迄今为止，其机理主要是基于各向同性介质中常见的热弹性膨胀，其适用性有限。在这项研究中，我们调查了概念上的光声效应的新机制，该机制涉及利用过渡金属_二硫代双氰化物VTe ₂的结构不稳定性带状电荷密度波（CDW）。超快电子显微镜成像和衍射测量揭示了与光致瞬时CDW溶解相关的纳米薄板中异常声波的产生和传播。我们的结果突出了光致结构不稳定性作为相干声波源的能力。