One might expect a one-dimensional metal to be rather simple: a string of equally spaced atoms whose valence electrons occupy a flat, featureless band. But in 1930 Rudolf Peierls found an interesting theoretical wrinkle.
Below a critical temperature, Peierls argued, the atoms of a 1D metal spontaneously acquire a periodic distortion that nudges them together in groups of two, three, or more. The energy cost of reordering the atoms is met by the valence electrons, which assemble in a coherent state called a charge-density wave (CDW). 1
For decades, Peierls’s idea remained untested, not least because 1D arrays of mutually attracting atoms tend to be thermodynamically unstable. But in the 1970s chemists succeeded in making bulk materials from molecular chains whose mutual coupling is strong enough to forestall thermodynamic instability yet weak enough to let the chains distort unhindered.
Physicists soon observed a host of interesting electronic properties in niobium...
