  An abrupt Mott metal-insulator transition (MIT) rather than the continuous
Hubbard MIT near a critical on-site Coulomb energy U/U_c=1 is observed for the
first time in VO_2, a strongly correlated material, by inducing holes of about
0.018% into the conduction band. As a result, a discontinuous jump of the
density of states on the Fermi surface is observed and inhomogeneity inevitably
occurs. The gate effect in fabricated transistors is clear evidence that the
abrupt MIT is induced by the excitation of holes.
