The open orbits of potassium

The high-field magnetoresistance of potassium, which fails to saturate, can be an intrinsic property only if the Fermi surface is multiply connected. Direct observation of open-orbit magnetoresistance peaks by Coulter and Datars confirms this theoretical principle. Since the Brillouin zone of potassium is only half full, and the Fermi surface is nearly spherical, open orbits can occur only if the translational symmetry of the crystal is broken by a charge-density-wave structure. The open-orbit distributions that result explain the observed magnetoresistance patterns.