Excitonic effects on coherent phonon dynamics in single wall carbon nanotubes
Excitonic effects on coherent phonon dynamics in single wall carbon nanotubes
复制标题
激子效应对单壁碳纳米管相干声子动力学的影响
DOI：
10.1103/physrevb.88.075440
复制
发表时间：
2013
影响因子：
3.7
通讯作者：
R. Saito
中科院分区：
文献类型：
--
作者：
A. R. T. Nugraha;E. I. Rosenthal;E. H. Hasdeo;G. D. Sanders;C. J. Stanton;M. S. Dresselhaus;R. Saito
我们讨论了激子如何影响单壁碳纳米管超快光谱中相干径向呼吸模式的产生。光激发激子在空间上具有局域性，在实际空间中产生空间分布的驱动力，该驱动力涉及激子-声子相互作用的多个声子波矢量。相干声子的运动方程用Klein-Gordon方程进行了现象学建模，我们求解了振荡幅度作为空间和时间的函数。通过平均计算每个纳米管长度的振幅，我们得到了与时间相关的相干声子振幅，类似于在一些泵浦探针实验中观察到的均匀振荡。我们将这一结果解释为，实验只能看到碳纳米管中相干声子振荡在光波长上的空间平均，微观细节被平均掉了。通过计算由相干声子振荡引起的宏观原子位移所产生的随时间的吸收光谱，我们的解释是合理的。计算得到的包含激子效应的相干声子谱在纳米管跃迁能处显示出实验观察到的对称峰，而不包括激子效应时则显示出不对称峰。
We discuss how excitons can affect the generation of coherent radial breathing modes in the ultrafast spectroscopy of single-wall carbon nanotubes. Photoexcited excitons can be localized spatially and give rise to a spatially distributed driving force in real space which involves many phonon wave vectors of the exciton-phonon interaction. The equation of motion for the coherent phonons is modeled phenomenologically by the Klein-Gordon equation, which we solve for the oscillation amplitudes as a function of space and time. By averaging the calculated amplitudes per nanotube length, we obtain time-dependent coherent phonon amplitudes that resemble the homogeneous oscillations that are observed in some pump-probe experiments. We interpret this result to mean that the experiments are only able to see a spatial average of coherent phonon oscillations over the wavelength of light in carbon nanotubes and the microscopic details are averaged out. Our interpretation is justified by calculating the time-dependent absorption spectra resulting from the macroscopic atomic displacements induced by the coherent phonon oscillations. The calculated coherent phonon spectra including excitonic effects show the experimentally observed symmetric peaks at the nanotube transition energies, in contrast to the asymmetric peaks that would be obtained if excitonic effects were not included.