Disorder-induced topological defects in a d=2 elastic medium at zero temperature

The density and correlations of topological defects are investigated numeri cally in a model of a d=2 elastic medium subject to a periodic quenched ran dom potential. The computed density of defects decreases approximately expo nentially with the defect core energy. Comparing the defect-free ground sta te with the ground state with defects, it is found that the difference is d escribed by stringlike excitations, bounded by defect pairs, which have a f ractal dimension of 1.250+/-0.003. At zero temperature, the disorder-induce d defects screen the interaction of introduced vortex pairs.