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arXiv 1408.0672cond-mat.mes-hall
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单壁碳纳米管中相干G带声子谱的起源

Origin of coherent G band phonon spectra in single wall carbon nanotubes

A. R. T. Nugraha, E. H. Hasdeo, G. D. Sanders, C. J. Stanton, R. Saito

摘要:

利用泵浦-探测光谱技术研究了单壁碳纳米管中的相干声子,发现相干声子的微分吸收系数随时间的变化。对于径向呼吸模式(RBM)的单壁碳纳米管,相干声子信号被理解为是由于相干RBM声子振荡调制的直径相关的能隙的结果。然而,这种机制可能不是占主导地位的贡献,在单壁碳纳米管的其他声子模式。特别是,对于G带声子,这对应于键拉伸运动,我们发现,原子间偶极矩阵元的调制引起的相干G带声子强度相媲美的相干RBM声子强度。我们还进一步讨论了相干G带和RBM声子振幅与激光激发脉宽的关系。

英文摘要:

Coherent phonons in single wall carbon nanotubes (SWNTs) are observed as oscillations of the differential absorption coefficient as a function of time by means of pump-probe spectroscopy. For the radial breathing mode (RBM) of a SWNT, the coherent phonon signal is understood to be a result of the modulated diameter-dependent energy gaps due to the coherent RBM phonon oscillations. However, this mechanism might not be the dominant contribution to other phonon modes in the SWNT. In particular, for the G band phonons, which correspond to bond-stretching motions, we find that the modulation of the interatomic dipole matrix element gives rise to a strong coherent G band phonon intensity comparable to the coherent RBM phonon intensity. We also further discuss the dependence of coherent G band and RBM phonon amplitudes on the laser excitation pulse width.

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