  Gapless spin liquids have recently been observed in several frustrated Mott
insulators, with elementary spin excitations - "spinons" - reminiscent of
degenerate Fermi systems. However, their precise role at the Mott point, where
charge fluctuations begin to proliferate, remains controversial and
ill-understood. Here we present the simplest theoretical framework that treats
the dynamics of emergent spin and charge excitations on the same footing,
providing a new physical picture of the Mott metal-insulator transition at half
filing. We identify a generic orthogonality mechanism leading to strong damping
of spinons, arising as soon as the Mott gap closes. Our results indicates that
spinons should not play a significant role within the high-temperature quantum
critical regime above the Mott point - in striking agreement with all available
experiments.
