Saddle point states in 2D superconducting film biased near the depairing current

Abstract

The structure and energy of saddle point (SP) states in 2D superconducting film of finite width $w$ with transport current $I$ are found in the framework of Ginzburg-Landau model. We show that very near depairing current $I_{dep}$ the SP state with a vortex does not exist and it transforms to 2D nucleus state, which is a finite region with partially suppressed order parameter. It is also shown that for slightly lower currents the contribution of the vortex core energy is important for SP state with a vortex and it cannot be neglected for $I\gtrsim 0.6 I_{dep}$. It is demonstrated that in the film with local current concentration near the bend the energy of SP state may be much smaller than one in the straight film and it favors the effect of fluctuations in such a samples.