啁啾中红外脉冲对非线性声子的有效激发：诱导结构相变
Efficient excitation of nonlinear phonons via chirped mid-infrared pulses: induced structural phase transitions
摘要：
非线性声子在强激光与固体相互作用中起着重要作用。我们讨论非线性动力学协议，允许有效的激发和控制的非线性声子。我们考虑了最近的一些令人鼓舞的建议：在顺电材料如KTaO $_3$中诱导铁电性和在铜酸盐如La $_2$ CuO $_4$中诱导结构变形[A. Subedi et.al，Phys.Rev.B89，220301（2014），A.Subedi，Phys.Rev.B95，134113（2017）]。高频声子模式由中红外脉冲驱动，并且耦合到低频模式，这些间接激发引起结构变形。这些建议与最近一系列关于光诱导相变的实验是一致的。我们研究了更详细的情况下，KTaO $_3$没有应变，其中（乍一看）它是不可能激发所需的低频声子模式的共振驱动的较高的频率。声子系统的行为解释使用耦合驱动非线性振子的简化模型。我们发现了一个动力学机制，防止有效的激励共振驱动，并表明，从确切的共振驱动频率的某些失谐的系统响应，违反直觉，大大放大。为了在KTaO $_3$中无应变地诱导铁电性，我们采用扫频驱动，实现所谓的捕获共振。该方法适用于现实的飞秒脉冲。我们的方法可以应用到其他相关的系统，例如激光驱动的正交钙钛矿像ErFeO $_3$。
英文摘要：
Nonlinear phononics play important role in strong laser-solid interactions. We discuss nonlinear dynamical protocols which allow for efficient excitation and control of nonlinear phonons. We consider recent inspiring proposals: inducing ferroelectricity in paraelectric material such as KTaO$_3$ and inducing structural deformations in cuprates like La$_2$CuO$_4$ [A. Subedi et.al, Phys. Rev. B 89,220301 (2014), A.Subedi, Phys. Rev. B 95, 134113 (2017)]. High-frequency phonon modes are driven by mid-infrared pulses, and coupled to lower-frequency modes those indirect excitation causes structural deformations. Such proposals are in line with a series of recent experiments on light-induced phase transitions. We study in a more detail the case of KTaO$_3$ without strain, where (at first glance) it was not possible to excite the needed low frequency phonon mode by resonant driving of the higher frequency one. Behaviour of the phonon system is explained using a reduced model of coupled driven nonlinear oscillators. We find a dynamical mechanism which prevents effective excitation at resonance driving, and show that for certain detunings of driving frequency from the exact resonance the system response is, counterintuitively, greatly amplified. In order to induce ferroelectricity in KTaO$_3$ without a strain we employ driving with sweeping frequency, realizing so called capture into resonance. The method works for realistic femtosecond pulses. Our approach can be applied to other related systems, e.g. laser driven orthorombic perovskites like ErFeO$_3$.
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