Exposing the static scale of the glass transition by random pinning

The dramatic slowing down associated with the glass transition cannot be fully understood without an associated static length that is expected to increase rapidly as the temperature is reduced. The search for such a length was long and arduous, without a universally accepted candidate at hand. Recently a natural such length $\xi_s$ was proposed, stemming from a cross-over between plastic and elastic mechanical responses of the material. In this Letter we show that supercooled liquids in which there exists random pinning sites of density $\rho_{\rm im}\sim 1/\xi_s^d$ exhibit complete jamming of all dynamics. This is a direct demonstration that the proposed length scale is indeed {\em the} static length that was long sought-after.