Simulation study on the first penetration field in type-II superconductors

On the basis of computer simulations of the time-dependent Ginzburg - Landau model including thermal noise effects, we evaluate the surface barrier against magnetic flux penetration in type-II superconductors. We discuss several parameter dependencies of the first field for flux penetration, which is estimated from the first peak position of the magnetization curve in the presence of an external field slowly increasing over time. It is shown that the first penetration field is a decreasing function of temperature and of the degree of sample shape deformation. The surface barrier is also found to be suppressed by the surface irregularity on the scale of the magnetic penetration depth.