Fermionic Retroreflection, Hole Jets and Magnetic Steering in 2D Electron Systems

Electron interactions are usually probed indirectly, through their impact on transport coefficients. Here we describe a direct scheme that, in principle, gives access to the full angle dependence of carrier scattering in 2D Fermi gases. The latter is particularly interesting, because, due to the dominant role of head-on collisions, carrier scattering generates tightly focused fermionic jets. We predict a jet-dominated signal for the magnetic steering geometry, that appears at classically weak $B$-fields, much lower than the free-particle focusing fields. The effect is "anti-Lorentz" in sign, producing a peak at the field polarity for which the free-particle focusing does not occur. The steering signal measured vs. $B$ yields detailed information on the angular structure of fermionic jets.