Hierarchical Coherent Phonons in a Superatomic Semiconductor
Hierarchical Coherent Phonons in a Superatomic Semiconductor
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DOI：
10.1002/adma.201903209
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发表时间：
2019-07
影响因子：
29.4
通讯作者：
Kihong Lee;S. Maehrlein;Xinjue Zhong;D. Meggiolaro;Jake C. Russell;Douglas A Reed;Bonnie Choi;F. De Angelis;Xavier Roy;Xiaoyang Zhu
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文献类型：
--
作者：
Kihong Lee;S. Maehrlein;Xinjue Zhong;D. Meggiolaro;Jake C. Russell;Douglas A Reed;Bonnie Choi;F. De Angelis;Xavier Roy;Xiaoyang Zhu
声子与电子和其他声子的耦合在材料特性中起着决定性作用，例如电荷和能量传输、光发射和超导性。在原子固体中，声子在 3D 晶格上离域，而分子固体则以局域振动为主。这里描述了一种分层半导体，它通过将局域 0D 模式与离域 2D 和 3D 模式相结合来扩展声子空间。这种材料由共价连接成二维片材的超原子构件 (Re6Se8) 组成，这些二维片材堆叠成分层的范德华晶格。使用瞬态反射光谱，识别出三种类型的相干声子：孤立超原子的局域 0D 呼吸模式、层中超原子的 2D 同步扭曲以及 3D 声学层间变形。这些声子在不同程度上耦合到电子自由度。扩展晶体中局部声子模式的存在为通过分层声子工程控制材料特性打开了大门。
The coupling of phonons to electrons and other phonons plays a defining role in material properties, such as charge and energy transport, light emission, and superconductivity. In atomic solids, phonons are delocalized over the 3D lattice, in contrast to molecular solids where localized vibrations dominate. Here, a hierarchical semiconductor that expands the phonon space by combining localized 0D modes with delocalized 2D and 3D modes is described. This material consists of superatomic building blocks (Re6Se8) covalently linked into 2D sheets that are stacked into a layered van der Waals lattice. Using transient reflectance spectroscopy, three types of coherent phonons are identified: localized 0D breathing modes of isolated superatom, 2D synchronized twisting of superatoms in layers, and 3D acoustic interlayer deformation. These phonons are coupled to the electronic degrees of freedom to varying extents. The presence of local phonon modes in an extended crystal opens the door to controlling material properties from hierarchical phonon engineering.