Quantum oscillations in the underdoped cuprate YBa₂Cu₄O₈

We report the observation of quantum oscillations in the underdoped cuprate superconductor YBa2Cu4O8 using a tunnel-diode oscillator technique in pulsed magnetic fields up to 85 T. There is a clear signal, periodic in inverse field, with frequency 660 +/- 15 T and possible evidence for the presence of two components of slightly different frequency. The quasiparticle mass is m*=3.0 +/- 0.3m(e). In conjunction with the results of Doiron-Leyraud et al. for YBa2Cu3O6.5, the present measurements suggest that Fermi surface pockets are a general feature of underdoped copper oxide planes and provide information about the doping dependence of the Fermi surface.