Large-amplitude chirped coherent phonons in tellurium mediated by ultrafast photoexcited carrier diffusion

Kamaraju, N. ; Kumar, Sunil ; Anija, M. ; Sood, A. K. (2010) Large-amplitude chirped coherent phonons in tellurium mediated by ultrafast photoexcited carrier diffusion Physical Review B: Condensed Matter and Materials Physics, 82 (19). 195202_1-195202_7. ISSN 1098-0121

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Official URL: http://prb.aps.org/abstract/PRB/v82/i19/e195202

Related URL: http://dx.doi.org/10.1103/PhysRevB.82.195202

Abstract

We report femtosecond time-resolved reflectivity measurements of coherent phonons in tellurium performed over a wide range of temperatures (3-296 K) and pump-laser intensities. A totally symmetric A1 coherent phonon at 3.6 THz responsible for the oscillations in the reflectivity data is observed to be strongly positively chirped (i.e., phonon time period decreases at longer pump-probe delay times) with increasing photoexcited carrier density, more so at lower temperatures. We show that the temperature dependence of the coherent phonon frequency is anomalous (i.e, increasing with increasing temperature) at high photoexcited carrier density due to electron-phonon interaction. At the highest photoexcited carrier density of ~1.4×1021 cm−3 and the sample temperature of 3 K, the lattice displacement of the coherent phonon mode is estimated to be as high as ~0.24 Å. Numerical simulations based on coupled effects of optical absorption and carrier diffusion reveal that the diffusion of carriers dominates the nonoscillatory electronic part of the time-resolved reflectivity. Finally, using the pump-probe experiments at low carrier density of 6×1018 cm−3, we separate the phonon anharmonicity to obtain the electron-phonon coupling contribution to the phonon frequency and linewidth.

Item Type:Article
Source:Copyright of this article belongs to American Physical Society.
ID Code:50233
Deposited On:22 Jul 2011 14:03
Last Modified:18 May 2016 04:36

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