Negative resistance and heat dissipation in superconducting wires in an ac magnetic field

A superconducting wire embedded into an alternating magnetic field H proportional to cos(omega t) can manifest negative resistance. At high enough frequencies omega greater than or similar to 1/z, where tau is the characteristic time of magnetic relaxation, this effect becomes prominent. As a result, the energy obtained by the wire from a source of magnetic field (external coil) is transformed into the electromotive force which reduces the external voltage required to keep the transport current in the wire. We show that negative resistance appears in line with the out-of-phase regime of the ac magnetic response, and both are related with the crucial inhibition of the vortex dynamics by zero-field (annihilation) lines. We also find a universal (independent of frequency) expression for the mean voltage in a wire.