When Is a Metal Not a Metal?

by Steven C. Erwin Nature, 18 May 2006 Every student knows the difference between a metal and an insulator: one conducts electricity and the other doesn't. Things get more interesting if you ask how this difference arises. Although the question is disarmingly simple, a rigorous answer was not available until about 1930, when Felix Bloch and Alan Wilson used the new quantum mechanics to create a theory that distinguished metals from insulators. The spectacular success of this 'band theory of solids', as it is now known, has made it a cornerstone of the modern theory of solids. In a few glaring cases, however, band theory doesn't get it right. Read more