08 April 2011
Vol 332, Issue 6026

About The Cover

Cover image expansion

COVER When certain materials drop below a critical temperature, they enter a superconducting phase characterized by zero electrical resistance. A readily visualized signature of the superconducting state is the ability to expel magnetic fields. In this photo, a magnet placed on top of the ceramic yttrium barium copper oxide levitates as the temperature drops below 123 kelvin and the material becomes superconducting. See the special section beginning on page 189. Photo: Takeshi Takahara/Photo Researchers, Inc.