Laboratoire Charles Coulomb UMR 5221 CNRS/UM2 (L2C)

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Spin dynamics in CdMnTe quantum wells

par Sébastien LAYSSAC - publié le , mis à jour le

Concerning spin dynamics, the most outstanding results were obtained on the dynamics of collective excitations in n-type CdMnTe quantum wells, in which we have observed in the time-domain the signature of mixed electron-Mn precession modes. This is an example of strong coupling between conduction band electron spins and Mn spins, which manifests itself via the appearance of spin beatings (see Figure 6). This observation gives a new independent mean to determine the spin polarisation of the 2DEG, and look for its enhancement due to Coulomb interactions. In addition Mn spin excitations uncoupled to the 2DEG have been discovered. This counterintuitive result could be interpreted and modelled in collaboration with Alexander Dimitriev during his visit in our laboratory supported by a CNRS grant. This work is also supported by the project GOSPININFO (2008-2011) coordinated by Florent Perez from INSP (programme Blanc 2007 n° BLAN07-2_187114), concerning the optical generation and detection of spin waves.
Our works will follow up our ongoing activity on collective excitations in CdMnTe quantum wells, in which several original results were obtained in our group (hot/cold magnetization domains, soft precession mode in p-doped quantum wells, mixed modes and uncoupled modes in n-doped quantum wells). We are also involved in the ANR project GOSPININFO, funded till 2011, with the task to demonstrate the generation and detection of spin waves using femtosecond optical pulses, and ultimately to demonstrate spin wave propagation.

Time-resolved Kerr rotation (black curve) and fit with 3 damped cosines (red curve) (left a). FFT of the Kerr rotation exhibiting the existence of three modes, two broadened mixed modes and one narrow uncoupled mode (left b)). Precession frequencies and relaxation times of the three modes as a function of magnetic field (right a and b). - © L2C

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