Number 205 (Story #1), December 1, 1994 by Phillip F. Schewe and Ben Stein COMPOSITE FERMIONS ARE REAL. At low temperature and in a high magnetic field, a two- dimensional gas of electrons (confined at the interface between two semiconductors) can exhibit the quantum Hall effect: as the magnetic field is increased, the Hall resistance (the voltage across the sample divided by the current) rises not linearly but in a series of discrete steps. In one manifestation of the phenomenon, the fractional quantum Hall effect, the strongly interacting electrons behave in a particularly complicated way. In an effort to avoid each other, they form a fluid which consists of electrons that have amalgamated with magnetic flux lines. That is, the electrons each assimilate an even number of magnetic vortices. This process has the effect of partially or totally "using up" the magnetic field. Furthermore, the resultant particles, called composite fermions, interact with each other very little. Recent experiments have shown that composite fermions have many of the properties of true particles: they have mass, execute cyclotron motions in the remaining magnetic field, and have definite energy levels. (J.K. Jain, Science, 18 November 1994.)