Thin granular layers are stronger, even without friction

The jamming transition is accompanied by a rich phenomenology such as hysteretic behaviors and non-local effects. These phenomena are often considered to be interrelated. Here, we investigate experimentally a model frictionless granular layer flowing down an inclined plane. This system provides a unique opportunity to disentangle the cause-effect relationships between this phenomena and decipher their origin. We find that (i) thin frictionless granular layers are devoid of hysteresis, yet the layer stability is increased as it gets thinner. These effects are thus independent. (ii) Rheological flow rules can be collapsed into a unique master curve, supporting that non-local effects correspond to the usual finite-size effects associated to the presence of a critical point. (iii) This collapse supports that the so-called isostatic length $l^*$ governs the effect of boundaries on flow, and rules out other propositions made in the past.