Quantum linear magnetoresistance

A description is presented of experimental results, old and new ones, in which a magnetoresistance was discovered, linear in magnetic field. It is explained that there are two theoretical possibilities for such a phenomenon. The first one happens in a polycrystalline metal in a classically large field; it was known since the late 1950s. The other one is the so-called "quantum magnetoresistance" in semimetals and in some single crystalline metals having small pockets of the Fermi surface with a small effective mass.