Spectroscopy of electron — electron scattering in a 2DEG

Experimentally electron-beam injection and detection via quantum point-contacts is used to investigate the scattering of a non-equilibrium electron distribution in a twodimensional electron gas (2DEG) of a GaAs/(Ga,Al)As heterostructure. The energy dependence of electron-electron scattering processes has been studied in a weak magnetic field by investigating the detector signal. Assuming electron beams with a narrow opening angle a magnetic field $B$ perpendicular to the 2DEG plane causes only electrons which are scattered in a point $O$ at an angle $\alpha$ to reach the detector. Thus, it is possible to measure directly the energy dependence of the angular electron distribution after scattering. The experimental data give a clear evidence for the importance of small angle scattering processes in two-dimensional systems, as predicted theoretically.