  We show theoretically that two-dimensional direct-gap semiconductors with a
valley degree of freedom, including monolayer transition-metal dichalcogenides
and gapped bilayer graphene, have a longitudinal magnetoconductivity
contribution that is odd in valley and odd in the magnetic field applied
perpendicular to the system. Using a quantum kinetic theory we show how this
valley-dependent magnetoconductivity arises from the interplay between the
momentum-space Berry curvature of Bloch electrons, the presence of a magnetic
field, and disorder scattering. We discuss how the effect can be measured
experimentally and used as a detector of valley polarization.
