Nonlinear Conductivity of a Holographic Superconductor Under Constant   Electric Field
  The dynamics of a two-dimensional superconductor under a constant electric field $E$ is studied by using the gauge/gravity correspondence. The pair breaking current induced by $E$ first increases to a peak value and then decreases to a constant value at late time, where the superconducting gap goes to zero, corresponding to a normal conducting phase. The peak value of the current is found to increase linearly with respect to the electric field. Moreover, the nonlinear conductivity, defined as an average of the conductivity in the superconducting phase, scales as $\sim E^{-2/3}$ for large $E$ when the system is close to the critical temperature, which agrees with predictions from solving the time dependent Ginzburg-Landau equation. 
Hua-Bi Zeng, Yu Tian, Zheyong Fan and Chiang-Mei Chen
hep-th