De Haas-van Alphen effect in single crystal MgB₂

We present an experimental study of the de Haas-van Alphen effect in single crystals of MgB₂, using a piezo-resistive torque technique. Three quasi-particle orbits were observed. Two originate from a single warped Fermi surface tube along the c direction, and the third from a cylindrical section of an in-plane honeycomb network. The quasi-particle effective masses on these orbits were determined and compared to band structure calculations. From this we deduce that the electron-phonon coupling strength λ, is a factor ∼3 larger for the c-axis tube orbits than for the in-plane network orbit, in accord with recent microscopic calculations.