semimetall

A semimetal is a solid material in which the conduction and valence bands either overlap slightly, or a very small indirect band gap exists, resulting in a small number of charge carriers at the Fermi level. This places semimetals between metals and semiconductors: they conduct like metals but with a relatively low carrier concentration.

In semimetals, both electrons and holes contribute to electrical transport. The carrier density is typically low, and the density of states at the Fermi level is reduced compared with ordinary metals, yet the materials can display metallic-like conductivity due to high carrier mobilities. Transport properties are often highly anisotropic and can be strongly influenced by temperature and impurities.

Classic elemental semimetals include bismuth and antimony, which exhibit unusual electronic structures and transport behavior. Graphite is another well-studied semimetal, characterized by a small overlap of its electronic bands. These materials often show phenomena such as large magnetoresistance and unusual thermoelectric responses, reflecting their low carrier densities and high mobilities.

In contemporary solid-state physics, the term semimetal also encompasses topological semimetals, such as Dirac and Weyl semimetals. These materials host relativistic-like quasiparticles near band crossings and possess distinctive surface states, attracting interest for fundamental science and potential applications in electronics, spintronics, and quantum devices.

Semimetal is a terminology used primarily in physics to describe electronic structure and transport behavior. It is distinct from the chemical category of metalloid, though many semimetals lie near the metalloid region of the periodic table.