脉冲光激发下纳米结构中的电子-声子温度反转
Electron-Phonon Temperature Inversion in Nanostructures under Pulsed Photoexcitation
AI总结：
本文通过三维有限元模拟和零维解析模型，揭示空间扩展纳米结构中电子-声子耦合系数存在最优范围，可导致晶格温度局部超过电子温度的温度反转现象，其中铂最显著，为超快光热控制设计提供指导。
摘要：
用短光脉冲光激发金属纳米结构可以驱动非热电子态，这些电子态在衰减后导致电子温度升高（$T_e \gtrapprox 1000\\,\mathrm{K}$），最终通过电子-声子散射与晶格（$T_p$）达到平衡。在这里，我们表明，在空间扩展的纳米结构中，晶格温度可以局部超过电子温度，这是一种看似违反直觉的瞬态效应，此后称为“温度反转”（$T_p > T_e$）。这一现象从根本上源于不均匀的吸收模式，在较小颗粒中不存在，它产生于电子-声子耦合与竞争性电子热扩散之间复杂的时空相互作用。通过将基于严格的三维（3D）有限元方法的模拟与实用的简化零维（0D）解析模型相结合，我们确定电子-声子耦合系数（$G_{e-p}$）是控制该行为的关键参数。存在一个最优的 $G_{e-p}$ 范围允许温度反转发生，而过弱或过强的耦合都会抑制它。在常见的等离激元金属中，铂（Pt）表现出最显著且持续时间最长的温度反转，而金（Au）和银（Ag）则没有明显的温度反转。此外，一旦选择了适当的特征长度，0D 和 3D 结果之间的高度一致性表明，控制温度反转的核心物理可以在没有完整空间复杂性的情况下被捕捉。这些结果为优化纳米尺度能量传递和热载流子驱动过程提供了见解，指导材料、几何结构和激发条件的策略性设计，以实现增强的超快光热控制。
英文摘要：
Photoexcitation of metallic nanostructures with short optical pulses can drive non-thermal electronic states, which, upon decay, lead to elevated electronic temperatures ($T_e \gtrapprox 1000\,\mathrm{K}$) eventually equilibrating with the lattice ($T_p$) through electron-phonon scattering. Here, we show that, in spatially extended nanostructures, the lattice temperature can locally exceed that of the electrons, a seemingly counterintuitive transient effect termed hereafter ``temperature inversion'' ($T_p > T_e$). This phenomenon, fundamentally due to inhomogeneous absorption patterns and absent in smaller particles, emerges from a complex spatio-temporal interplay, between the electron-phonon coupling and competing electronic thermal diffusion. By combining rigorous three-dimensional (3D) finite-element-method-based simulations with practical reduced zero-dimensional (0D) analytical models, we identify the electron-phonon coupling coefficient ($G_{e-p}$) as the critical parameter governing this behavior. An optimal $G_{e-p}$ range allows the inversion, whereas a weak or overly strong coupling suppresses it. Among common plasmonic metals, platinum (Pt) exhibits the most pronounced and long-lived inversion, while gold (Au) and silver (Ag) show no significant inversion. Moreover, the close agreement between the 0D and 3D results, once an appropriate characteristic length is selected, highlights that the essential physics governing the inversion can be captured without full spatial complexity. These results provide insights for optimizing nanoscale energy transfer and hot-carrier-driven processes, guiding the strategic design of materials, geometries, and excitation conditions for enhanced ultrafast photothermal control.
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