Nonlinear effects during vortex motion at high velocities

The nonequilibrium quasiparticle distribution effected in the superconducting mixed state at high vortex velocities leads to highly nonlinear current-voltage (IV) characteristics, as discussed theoretically by Larkin and Ovchinnikov. In the temperature regime near T-c, at a maximum vortex velocity upsilon(phi)* an electronic instability takes place and the sample switches into a state with higher electric resistivity. observed using epitaxial c-axis oriented films of YBa2Cu3O7-delta. In the temperature regime T << T-c a logarithmic singularity appears in the IV characteristics at an electric current I*, which originates from the contraction of the vortex core first discussed by Kramer and Pesch. This singularity has been observed in epitaxial c-axis oriented Nd1.85Ce0.15CuOx films. Both effects, at T approximate to T-c and T << T-c depend sensitively on the inelastic quasiparticle scattering rate tau(in)(-1), and experimental values of tau(in)(-1) as a function of temperature can be extracted from these experiments.