De Haas–van Alphen Effect in Single Crystal [Formula presented]

We report observations of quantum oscillations in single crystals of the high temperature superconductor [Formula presented]. Three de Haas–van Alphen frequencies are clearly resolved. Comparison with band structure calculations strongly suggests that two of these come from a single warped Fermi surface tube along the [Formula presented] direction, and that the third arises from cylindrical sections of an in-plane honeycomb network. The measured values of the effective mass range from [Formula presented]. By comparing these to calculated band masses, we find that the electron-phonon coupling strength [Formula presented] is a factor of [Formula presented] larger for the [Formula presented]-axis tube orbits than for the in-plane network orbit, in accord with recent microscopic calculations.