Europhys. Lett., 70 (3), pp. 390-396 (2005)
DOI: 10.1209/epl/i2005-10010-x

Fast decoherence of slowly relaxing polarons in semiconductor quantum dots

F. Bras¹, S. Sauvage¹, G. Fishman¹, P. Boucaud¹, J.-M. Ortega² and J.-M. Gérard<sup>3

1</sup>  Institut d'Électronique Fondamentale, UMR CNRS 8622, Bâtiment 220 Université Paris-Sud - 91405 Orsay, France
²  CLIO-Lure, Bâtiment 209 D, Université Paris Sud - 91405 Orsay, France
³  CEA-Grenoble, DRFMC-PSC - 38054 Grenoble Cedex 9, France

philippe.boucaud@ief.u-psud.fr

received 11 February 2005; accepted in final form 21 March 2005
published online 8 April 2005

Abstract
We report on polaron dynamic measurements in semiconductor quantum dots. The polaron dynamics is monitored by transient nonlinear spectroscopy by recording the transmission variation as a function of the pulse area of an infrared picosecond excitation. A non-monotonous transmission is observed for pulse areas larger than a pulse. We attribute this transmission dependence with pulse area to a signature of damped optical Rabi oscillation of polarons. The damping of the Rabi oscillation is modeled by two level optical Bloch equations. A short dephasing time T₂ around 5 is deduced for the resonantly excited polaron, one order of magnitude smaller than the relaxation time. We show that the decoherence of the polaron state is not limited by its slow relaxation but rather by the fast dephasing of its phonon component.

PACS
78.67.Hc - Quantum dots.
78.47.+p - Time-resolved optical spectroscopies and other ultrafast optical measurements in condensed matter.
71.38.-k - Polarons and electron-phonon interactions.

© EDP Sciences 2005