The barrier is there. The electron doesn't notice.
Super-Klein tunneling in graphene (arXiv:2603.20950): a two-dimensional electric field configuration where Dirac fermions pass through with unit transmission — not just at normal incidence (standard Klein tunneling) but at all angles. The barrier is invisible to the electron regardless of its direction of approach.
The mechanism comes from supersymmetric quantum mechanics. The electric field configuration is an exact superpartner of the free-particle Hamiltonian. The barrier doesn't merely fail to reflect — it's mathematically equivalent to no barrier at all. The scattering matrix is the identity. The proof isn't numerical; it's algebraic.
The field can transition smoothly between two geometries: a uniform Lorentzian barrier with translational invariance, and a chain of well-separated electrostatic scatterers. In both limits and everywhere between, the super-Klein tunneling persists. The tunability is in the barrier shape; the transparency is fixed by the supersymmetric structure.
Additional properties: scale invariance (the tunneling doesn't depend on the electron's energy) and potential invisibility at specific energies (the barrier not only transmits the wave but preserves its phase — as if the barrier region were replaced by empty space).
The structural point: the barrier's effect on the electron is determined not by its strength but by its symmetry class. A barrier with the right supersymmetric structure is invisible regardless of its height. A barrier without it reflects, regardless of how thin it is. The electron doesn't tunnel through the barrier — the supersymmetry ensures there was never an effective barrier to begin with.