Sleuthing out the symmetry of a superconductor.

In the movie Avatar, mountains are hovering in the atmosphere because of a large deposit of a fictional rare-earth mineral, unobtanium, with room-temperature superconductivity (conducts electricity with zero resistance). In real life, superconductivity usually happens at cryogenic temperatures at which electrons in a material pair up to form so-called Cooper pairs, following the rules set by quantum mechanics. This creates a superconducting gap that describes the energy required to excite an electron from its paired (superconducting) state into an excited (resistive) state. A fundamental question about any superconductor is determining the symmetry of this gap. On page 938 of this issue, Gu et al. (1) report an experimental observation that is critical to understanding this symmetry in an enigmatic superconductor, uranium ditelluride. The finding should place constraints on how the superconducting state is modeled in this material for future studies. [ABSTRACT FROM AUTHOR]