  We study quantum phase coherence and weak localization (WL) in disordered
metals with restricted back-scattering and phenomenologically formulate a large
class of unconventional transport mechanisms as modified diffusion processes
not captured by the Boltzmann picture. Inspired by conductivity measurements in
ferromagnetic films and semiconductors where anomalous power law corrections
have been observed, we constrain memory dependent, self avoidance effects onto
the quantum enhanced back-scattered trajectories, drastically altering the
effect of weak localization in two dimensions (2D). Scale dependent corrections
to the conductivity fail to localize the electrons in $d \ge 2$ for
sufficiently weak disorder. Additionally, we analyze quantum transport in
reaction-diffusion systems governed by the Fisher's equation and observe
asymptotically similar delocalization in 2D. Such unconventional transport
might be relevant to certain non-Fermi liquid or strongly correlated phases in
2D within the negative compressibility regime.
