de Haas–van Alphen Effect in Single CrystalMgB2

Abstract

We report observations of quantum oscillations in single crystals of the high temperature superconductor ${\mathrm{MgB}}_2$. 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 $c$ direction, and that the third arises from cylindrical sections of an in-plane honeycomb network. The measured values of the effective mass range from $(0.44–0.68)m_e$. By comparing these to calculated band masses, we find that the electron-phonon coupling strength $\lambda$ is a factor of $\sim 3$ larger for the $c$-axis tube orbits than for the in-plane network orbit, in accord with recent microscopic calculations.