Coulomb interactions and delocalization in quantum Hall constrictions

We study a geometry-dependent effect of long-range Coulomb interactions on quantum Hall (QH) tunneling junctions. In an X-shaped geometry, duality relates junctions with opening angles alpha and (pi - alpha). We prove that duality between weak tunneling and weak backscattering survives in the presence of long range interactions, and that their effects are precisely cancelled in the self dual geometry alpha=pi/2. Tunneling exponents as a function of alpha, the interaction strength chi, and the filling fraction nu are calculated. We find that Coulomb interaction induces localization in narrow channels (large alpha), and delocalization for sharply pinched constrictions (small alpha). Consequently, an insulator to metal transition happens at an angle alpha_c(chi,nu) <=pi/2. We discuss the implications of our results for tunneling experiments in QH-constriction and cleaved-edge geometries.