One of the parameters characterizing the dynamics of vortices in superconductors is their inertial mass. Despite its importance, the determination of the vortex mass is a long-standing problem and remains a controversial issue. Since the pioneering work by Suhl in 1965 several different theoretical approaches for mass calculations were implemented, giving predictions which differ by 5 orders of magnitude. Despite the wide interest of the theoretical community, the mass of an individual vortex was never experimentally measured.

We have combined magneto-optical imaging with an ultra-fast heating/cooling technique to measure the movement of individual vortices in a superconducting film. The motion took place while the film was heated close to T_c where pinning and viscous forces are relatively small. Under these conditions, the dominant force is the magnetic repulsion between vortices. The extent of the motion of individual vortices is consistent with a vortex mass of few electronic masses per lattice constant at 0.97T_c.