Conductors have overlapping valence and conduction bands and thus do not have a band gap. Electrons are able to move through the conductor without much resistance because of the overlap of the two bands. Conductors are useful for transferring electricity from one location to another and are mostly used in electronics applications. Silver, copper, gold are some of the best natural conductors because they have low resistance, 1.59 x 10-8,1.68 x 10-8, and 2.44×10-8 Ωm respectively. Copper is most commonly used to conduct electricity since it is the cheaper than gold or silver but aluminum (2.82×10−8 Ωm) is used in some applications, such as high-voltage overhead wires, even though it has more resistance because it is lighter and cheaper than copper.1
Low resistivity is an important property for a conductor because if the resistivity is high the electricity running through the material will lose energy. This is critical when considering transporting energy from a power plant to a city, for example. The farther away the city, the more the electricity will cost. To solve this problem many researchers are investigating materials called “super conductors” which have zero resistance and could theoretically allow 100% efficient electricity transport. Breakthroughs in superconductivity have led to five Nobel Prizes in 1913, 1972, 1973, 1987, and 2003.2 Super conductors also have applications apart from electric power transmission. Common superconducting materials are YBa2Cu3O7 (YBCO), niobium-titanium, and niobium-tin. YBCO is easy to make and is often used to demonstrate superconductive properties but is not suitable more most practical applications. Niobium-titanium and niobium-tin are currently used as powerful electromagnets for MRI and NMR instruments. Applications that may be possible in the future include supercomputing and levitating trains. This video shows some of the applications of semiconductors https://www.youtube.com/watch?v=2xOAb68agy0
Graphene is another material that has low resistivity. With a resistivity of 1 x10-8 Ωm, graphene is a better conductor than any silver, or any other metal on the periodic table. Graphene is composed of a single sheet of carbon atoms and can be difficult to make in large quantities so it doesn’t have any commercial uses right now, but it is a promising material for electronic storage and photovoltaics in the future.