de Haas—van Alphen measurements of the Fermi surface in orderedCu3Au

We report the observation of de Haas—van Alphen oscillations in ordered ${\mathrm{Cu}}_3$Au. Data were taken in fields up to 90 kG and temperatures between 0.9 and 1.3 K. The results obtained are in very good agreement with a recent band-structure calculation. The shape of the closed electron piece in the fourth Brillouin zone was determined exactly by using the inversion scheme developed by Mueller et al. The radius of the neck orbit, which appears again remapped in the fourth Brillouin zone, is in surprising agreement with the rigid-band value. The superlattice band gap is approximately 0.04 Ry. Since large sections of the Fermi surface are close to the superlattice zone planes, a charge-density-wave-like mechanism could well be responsible for the order-disorder transformation.