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Nonthermal Transport of Energy Driven by Photoexcited Carriers in Switchable Solid States ofGeTe
Physical Review Applied ( IF 3.8 ) Pub Date : 2021-07-22 , DOI: 10.1103/physrevapplied.16.014055
R. Gu 1 , T. Perrault 1 , V. Juvé 1 , G. Vaudel 1 , M. Weis 1 , A. Bulou 1 , N. Chigarev 2 , A. Levchuk 1 , S. Raetz 2 , V.E. Gusev 2 , Z. Cheng 3 , H. Bhaskaran 3 , P. Ruello 1
Affiliation  

Phase-change alloys have seen widespread use, from rewritable optical disks to current interest in their use in emerging neuromorphic computing architectures. In spite of this enormous commercial interest, the physics of the carriers in these materials is still not fully understood. Here, we describe the time and space dependence of the coupling between photoexcited carriers and the lattice in both the amorphous and crystalline states of one phase-change material, GeTe. We study this material using a time-resolved optical technique called the picosecond acoustic method to investigate the in situ thermally assisted amorphous-to-crystalline phase transformation in GeTe. Our work reveals a clear evolution of electron-phonon coupling during the phase transformation, as the spectra of photoexcited acoustic phonons in the amorphous (a-GeTe) and crystalline (α-GeTe) phases are different. In particular, and surprisingly, our analysis of the photoinduced acoustic pulse duration in crystalline GeTe suggests that part of the energy deposited during the photoexcitation process takes place over a distance that clearly exceeds that defined by the skin depth of the pump light. Alternatively, the photoexcitation process remains localized within that skin depth in the amorphous state. We then demonstrate that this is due to supersonic diffusion of photoexcited electron-hole plasma in the crystalline state. Consequently, these findings prove the existence of the nonthermal transport of energy, which is much faster than lattice heat diffusion.

中文翻译:

GeTe 可切换固态中由光激发载流子驱动的能量非热传输

相变合金已被广泛使用,从可重写光盘到目前对其在新兴神经形态计算架构中使用的兴趣。尽管具有巨大的商业利益,但这些材料中载流子的物理性质仍未完全了解。在这里,我们描述了一种相变材料的非晶态和晶态中光激发载流子与晶格之间耦合的时间和空间依赖性,. 我们使用称为皮秒声学方法的时间分辨光学技术研究这种材料,以研究原位热辅助非晶到晶相转变. 我们的工作揭示了相变过程中电子-声子耦合的明显演变,因为非晶态中光激发声子的光谱(一种——) 和结晶 (α——) 阶段不同。特别是,令人惊讶的是,我们对晶体中光致声脉冲持续时间的分析表明在光激发过程中沉积的部分能量发生在明显超过泵浦光趋肤深度定义的距离上。或者,光激发过程保持在无定形状态的趋肤深度内。然后我们证明这是由于光激发电子空穴等离子体在结晶状态下的超音速扩散。因此,这些发现证明了能量的非热传输的存在,这比晶格热扩散快得多。
更新日期:2021-07-22
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