SmB6: Kondo insulator or exotic metal?

High pressure resistivity and Hall effect measurements on Sm${\mathrm{B}}_{6}$ show that the activation gap \ensuremath{\Delta} vanishes discontinuously between 45 and 53 kbar, yielding at high pressures a mass-enhanced Fermi liquid phase. The low temperature transport is dominated by extended states in the gap with unusual superunitarity scattering properties, and a carrier density which grows almost exponentially with reduced \ensuremath{\Delta}, saturating below 45 kbar near 0.15 electron per unit cell. Our results are inconsistent with hybridization gap models and suggest a striking parallel to Mott-Hubbard insulators.