These transitions can be achieved by tuning various ambient parameters such as temperature,[1] pressure[2] or, in case of a semiconductor, doping.
The basic distinction between metals and insulators was proposed by Hans Bethe, Arnold Sommerfeld and Felix Bloch in 1928-1929.
However, in 1937 Jan Hendrik de Boer and Evert Verwey reported that many transition-metal oxides (such as NiO) with a partially filled d-band were poor conductors, often insulating.
Due to the interaction the electrons would then feel a strong Coulomb repulsion, which Mott argued splits the band in two.
For a material to be a metal, the excitation frequency (ω) must be zero by definition,[2] which then gives us the static dielectric constant,
The polarization catastrophe model also theorizes that, with a high enough density, and thus a low enough molar volume, any solid could become metallic in character.