  The use of quantum entanglement to study condensed matter systems has been
flourishing in critical systems and topological phases. Additionally, using
real-space entanglement entropies and entanglement spectra one can characterize
localized and delocalized phases of disordered fermion systems. Here we instead
propose the momentum-space entanglement spectrum as a means of characterizing
disordered models. We show that localization in 1D arises from the momentum
space entanglement between left and right movers and illustrate our methods
using explicit models with spatially correlated disorder that exhibit phases
which avoid complete Anderson localization. The momentum space entanglement
spectrum clearly reveals the location of delocalized states in the energy
spectrum and can be used as a signature of the phase transition between a
delocalized and localized phase.
