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首页> 外文期刊>Physical Review X >Squeezed Thermal Phonons Precurse Nonthermal Melting of Silicon as a Function of Fluence
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Squeezed Thermal Phonons Precurse Nonthermal Melting of Silicon as a Function of Fluence

机译：压缩热声子使硅的非热熔融与注量成函数关系

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A femtosecond-laser pulse can induce ultrafast nonthermal melting of various materials along pathways that are inaccessible under thermodynamic conditions, but it is not known whether there is any structural modification at fluences just below the melting threshold. Here, we show for silicon that in this regime the room-temperature phonons become thermally squeezed, which is a process that has not been reported before in this material. We find that the origin of this effect is the sudden femtosecond-laser-induced softening of interatomic bonds, which can also be described in terms of a modification of the potential energy surface. We further find in ab?initio molecular-dynamics simulations on laser-excited potential energy surfaces that the atoms move in the same directions during the first stages of nonthermal melting and thermal phonon squeezing. Our results demonstrate how femtosecond-laser-induced coherent fluctuations precurse complete atomic disordering as a function of fluence. The common underlying bond-softening mechanism indicates that this relation between thermal squeezing and nonthermal melting is not material specific.
机译：飞秒激光脉冲可以沿热力学条件下无法到达的路径诱导各种材料的超快速非热融化，但尚不清楚在刚好低于融化阈值的注量下是否存在任何结构修饰。在这里，我们为硅显示在这种状态下，室温声子会受到热挤压，这是该材料以前从未报道过的过程。我们发现，这种影响的起因是飞秒激光诱导的原子间键的突然软化，这也可以通过势能表面的修饰来描述。我们还在从头到尾的激光激发势能表面分子动力学模拟中发现，在非热熔融和热声子压缩的第一阶段，原子沿相同的方向运动。我们的研究结果证明了飞秒激光引起的相干波动是作为能量密度函数完全顺应原子完全无序的原因。常见的潜在键软化机制表明，热挤压和非热熔融之间的这种关系不是特定于材料的。

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