Optically excited structural transition in atomic wires on surfaces at the quantum limit
Optically excited structural transition in atomic wires on surfaces at the quantum limit
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DOI：
10.1038/nature21432
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发表时间：
2017-04-13
期刊：
影响因子：
64.8
通讯作者：
Schmidt, W. G.
中科院分区：
文献类型：
--
作者：
Frigge, T.;Hafke, B.;Schmidt, W. G.
对固体的原子势能景观的瞬时控制可能导致新的物质状态，并在晶格振动的时间尺度上对核运动进行量子控制。最近开发的超快时间分辨衍射技术（1）将超快时间操纵与原子尺度空间分辨率和飞秒时间分辨率结合起来，联合收割机。这些进展使研究光致结构变化的散装固体，往往发生在时间尺度短至几百飞秒（2-6）。相反，在表面和单原子层（如石墨烯）上的实验报告了更长数量级的结构变化的时间尺度（7-9）。这就提出了一个问题，即低维材料对飞秒激光激发的结构响应是否通常是有限的。在这里，我们表明，从低到高对称状态的电荷密度波在原子铟（In）线支持的硅（Si）表面的光诱导跃迁发生在350飞秒。光激发破坏并产生In-In键，导致软声子模式的非热激发，并通过这些软声子模式与多种表面和界面声子的耦合来驱动临界阻尼核运动极限下的结构转变。硅表面对称性破缺。这一发现表明，仔细调谐的电子激发可以产生非平衡势能面，在量子极限（即，在核运动是定向和确定性的状态下）驱动界面处的结构动力学（8）。这种技术可以潜在地用于调谐固体对光激发的动态响应，并且具有广泛的潜在应用，例如在超快探测器中（10，11）。
Transient control over the atomic potential-energy landscapes of solids could lead to new states of matter and to quantum control of nuclear motion on the timescale of lattice vibrations. Recently developed ultrafast time-resolved diffraction techniques(1) combine ultrafast temporal manipulation with atomic-scale spatial resolution and femtosecond temporal resolution. These advances have enabled investigations of photo-induced structural changes in bulk solids that often occur on timescales as short as a few hundred femtoseconds(2-6). In contrast, experiments at surfaces and on single atomic layers such as graphene report timescales of structural changes that are orders of magnitude longer(7-9). This raises the question of whether the structural response of low-dimensional materials to femtosecond laser excitation is, in general, limited. Here we show that a photo-induced transition from the low-to high-symmetry state of a charge density wave in atomic indium (In) wires supported by a silicon (Si) surface takes place within 350 femtoseconds. The optical excitation breaks and creates In-In bonds, leading to the non-thermal excitation of soft phonon modes, and drives the structural transition in the limit of critically damped nuclear motion through coupling of these soft phonon modes to a manifold of surface and interface phonons that arise from the symmetry breaking at the silicon surface. This finding demonstrates that carefully tuned electronic excitations can create non-equilibrium potential energy surfaces that drive structural dynamics at interfaces in the quantum limit (that is, in a regime in which the nuclear motion is directed and deterministic)(8). This technique could potentially be used to tune the dynamic response of a solid to optical excitation, and has widespread potential application, for example in ultrafast detectors(10,11).