  The fundamental interactions between an edge dislocation and a random solid
solution are studied by analyzing dislocation line roughness profiles obtained
from molecular dynamics simulations of Fe0.70Ni0.11 Cr0.19 over a range of
stresses and temperatures. These roughness profiles reveal the hallmark
features of a depinning transition. Namely, below a temperature-dependent
critical stress, the dislocation line exhibits roughness in two different
length scale regimes which are divided by a so-called correlation length. This
correlation length increases with applied stress and at the critical stress
(depinning transition or yield stress) formally goes to infinity. Above the
critical stress, the line roughness profile converges to that of a random noise
field. Motivated by these results, a physical model is developed based on the
notion of coherent line bowing over all length scales below the correlation
length. Above the correlation length, the solute field prohibits such coherent
line bow outs. Using this model, we identify potential gaps in existing
theories of solid solution strengthening and show that recent observations of
length-dependent dislocation mobilities can be rationalized.
