Spin dynamics and lifetime of exciton polaritons in CuCl H. Rahimpour Soleimani, S. Cronenberger, O. Cre ´gut, J.-P. Likforman, M. Gallart, T. Ostatnicky, P. Gilliot, B. Ho ¨nerlage * IPCMS, UMR 7504 CNRS-ULP, B.P. 43, 23 Rue du Lœss, 67034 Strasbourg, France Available online 3 March 2005 Abstract In CuCl, biexcitons may be excited from the semiconductor ground state by two circularly polarized exciton polaritons of opposite helicity. We use this property to develop a new method in order to determine the spin-relaxation dynamics by means of non-degenerate pump–probe experiments. A pump beam first excites a spin-polarized exciton population. Then, we measure the induced absorption of a circularly polarized probe beam at the exciton biexciton transition. It depends on its polarization and the induced absorption dynamics gives information on the spin state of the exciton polariton population. When comparing results obtained in a (s + s + ) configuration with that of a (s + s  ) configuration, we determine the time evolution of the pseudo-spin of the exciton polaritons as well as their lifetime. # 2005 Elsevier B.V. All rights reserved. Keywords: Exciton-spin dynamics; Spin flip; CuCl 1. Introduction During the past decade, the spin-relaxation processes of electron, holes and excitons have been intensively studied in III–V and II–VI semiconductors and in other materials in order to specify the mechanisms, responsible for the time evolution of the total angular momentum (or pseudo-spin) of an excited state. To our knowledge, such studies have not been performed on I–VII compounds up to now. It is important to understand this dynamics, since the pseudo-spin can carry and store information on quite long time scales [1–4]. Spin-relaxation times are in general longer than optical coherence times and comparable to population lifetimes of electronic excitations. Direct large band gap semiconductors show very high absorption coefficients a = 10 5 cm 1 close to their band edge. Therefore, spin-relaxation times cannot be determined in such bulk material by classical methods as, for example, degenerate pump– probe experiments [5–7], time-resolved Faraday rotation [8,9] or time-resolved photoluminescence measurements [10–12]. In this publication, we present a method to determine the spin-relaxation dynamics through induced absorption in non-degenerate pump– probe experiments. We apply this technique to CuCl, www.elsevier.com/locate/apsusc Applied Surface Science 247 (2005) 107–114 * Corresponding author. E-mail address: Bernd.Honerlage@ipcms.u-strasbg.fr (B. Ho ¨nerlage). 0169-4332/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2005.01.130