Experimental confirmation of a intraband gap

The electrical-transport, magnetic, and structural properties of the antiferromagnetic semiconductor (Formula presented) have been probed by resistance, (Formula presented) Mössbauer spectroscopy, and x-ray-diffraction measurements to ∼30 GPa in a diamond-anvil cell. The pertinent results of this work are that a semiconductor-metal transition occurs at (Formula presented) while the (Formula presented) magnetic moments remain unaltered across the transition. To the highest pressure of 30 GPa, the relative volume of the unit cell decreases to (Formula presented) with no structural symmetry modification of the (Formula presented)-type unit cell. At and above (Formula presented) a magnetic hyperfine spectrum comprised of a single component with a non-negligible quadrupole interaction is evident below spin-ordering temperatures (Formula presented) No drastic or discontinuous change occurs in both the hyperfine field (Formula presented) and isomer shift at pressures encompassing (Formula presented) suggesting that the (Formula presented) electronic state is unchanged upon metallization. This is considered compelling experimental evidence for closure of a (Formula presented) gap within the ligand band manifold, and therefore is the mechanism responsible for the onset of a metallic state.