semimetallic

Semimetallic is an adjective describing materials or behaviors that lie between metals and semiconductors in their electronic structure. In a semimetal, the valence band maximum and the conduction band minimum either overlap slightly in energy or are separated by a very small indirect gap. This results in a very small density of states at the Fermi level and the presence of both electron and hole carriers at low energies.

Materials with semimetallic electronic structure typically show metallic conductivity but with distinctive transport properties. They often exhibit low carrier density compared with ordinary metals, high carrier mobility in some directions, and transport phenomena that are sensitive to crystal orientation. Magnetic fields can induce pronounced magnetoresistance and quantum oscillations, and the detailed behavior reflects the shape of the Fermi surface and the degree of band overlap or small gap.

Classic examples of semimetals include bismuth, graphite, arsenic, and antimony. In recent years, the term has been broadened by families such as Dirac semimetals and Weyl semimetals, which host linear band crossings and relativistic-like quasiparticles. Semimetallic behavior can also arise in narrow-gap or pressure-tuned materials, where slight changes to structure or composition move the system toward metallic or semiconducting limits.