de Haas–van Alphen effect in the vortex state ofNb3Sn

De Haas–van Alphen (dHvA) oscillations corresponding to five extremal areas of the Fermi surface have been observed in the vortex state of ${\mathrm{Nb}}_3$Sn, in magnetic fields as low as ∼0.5${\mathit{B}}_{\mathit{c}2}$. Both the dHvA frequencies and effective masses are unchanged from their values in the normal state, although the quantum oscillations experience a field-dependent additional damping in the superconducting state. The results show that the Landau quantization of quasiparticles persists in the mixed state of a clean type-II superconductor.