The propagation of electronic excitations along chiral quantum Hall edge channels has been thoroughly studied in the recent years in new electron optics experiments exploiting electron/photon analogies in this system. As examples, the electronic versions of Mach-Zehnder [1] or Hanbury Brown and Twiss [2] interferometers have been realized. However, contrary to photons, electrons interact with each other through the Coulomb interaction which strongly affects the coherence properties of electronic sources. In particular, at filling factor $\nu=2$, the dominant interaction mechanism results from the capacitive coupling between copropagating edge channels, as reported in Mach-Zehnder interferometers [3,4], and confirmed by energy relaxation measurements [5].

In this experiment, we investigate the coupling between two copropagating edge channels by measuring, in a wide frequency range going from 0.7 to 11 GHz, the transmission of charge density waves (or edge magnetoplasmons) from one edge to the other. A mesoscopic capacitor [6] is used to excite edge-magnetoplasmons of variable frequency, selectively in the outer channel and the resulting current in the inner channel is then collected after interaction on a length of a few microns. Damped charge oscillations between channels are observed, which can be explained by the existence of two eigenmodes of different velocities resulting from the interchannel coupling. The fast mode is a charge mode while the slow one is a neutral spin mode. Our experimental results are compared with theoretical models [7,8] providing a quantitative understanding of the coupling between the two edge channels and the resulting separation between the charge and neutral modes.

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[5] Le Sueur, H., Altimiras, C., Gennser, U., Cavanna, A., Mailly, D., Pierre, F., Physical Review Letters 105(5), 056803 (2010).

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