Numerical study of the strongly screened vortex glass model in an external field

The vortex glass model for a disordered high-T_c superconductor in an external magnetic field is studied in the strong screening limit. With exact ground state (i.e. T=0) calculations we show that 1) the ground state of the vortex configuration varies drastically with infinitesimal variations of the strength of the external field, 2) the minimum energy of global excitation loops of length scale L do not depend on the strength of the external field, however 3) the excitation loops themself depend sensibly on the field. From 2) we infer the absence of a true superconducting state at any finite temperature independent of the external field.