A new paradigm of universal Fano factor on and off conductance plateaus in quantum Hall systems: experiment and theory

The orthodox framework to account for shot noise in quantum transport relies on electron beam partitioning. This is the case for quantum Hall (QH) platforms in the presence of a quantum point contact (QPC). Consequently one expects vanishing noise on a conductance plateau, where each chiral edge mode is either fully transmitted or entirely backscattered, hence no beam partitioning. Surprisingly, recent experiments on diverse quantum Hall phases and disparate geometries reveal on-the-plateau shot noise with the Fano factor being equal to the bulk filling fraction (rather than the quasi-particle charge).

To account for these observations we present a new theoretical paradigm of shot noise that relies on the ubiquitous presence of counter-propagating neutral edge modes (``neutralons") at the edge. These neutrals may be of either a topological (hole-like filling fractions) or edge reconstruction (particle-like or integer filling fractions) origin. We show that even on an intermediate transmission plateau within the QPC shot noise can be generated via creating and then annihilating neutralons, leading to a Fano factor which is equal to the bulk filling fraction. This Fano factor remains robust even off the conductance plateau.