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

Kamaraju, N and Kumar, Sunil and Anija, M and Sood, AK (2010) Large-amplitude chirped coherent phonons in tellurium mediated by ultrafast photoexcited carrier diffusion. In: Physical Review B: Condensed Matter and Materials Physics, 82 (19).

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

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 A(1) 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 x 10(21) cm(-3) and the sample temperature of 3 K, the lattice displacement of the coherent phonon mode is estimated to be as high as similar to 0.24 angstrom. 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 x 10(18) cm(-3), we separate the phonon anharmonicity to obtain the electron-phonon coupling contribution to the phonon frequency and linewidth.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to The American Physical Society.
Department/Centre: Others
Division of Physical & Mathematical Sciences > Physics
Date Deposited: 08 Dec 2010 11:05
Last Modified: 08 Dec 2010 11:05
URI: http://eprints.iisc.ernet.in/id/eprint/34305

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