  A novel large-scale dynamo mechanism, the magnetic shear-current effect, is
discussed and explored. The effect relies on the interaction of magnetic
fluctuations with a mean shear flow, meaning the saturated state of the
small-scale dynamo can drive a large-scale dynamo -- in some sense the inverse
of dynamo quenching. The dynamo is nonhelical, with the mean-field $\alpha$
coefficient zero, and is caused by the interaction between an off-diagonal
component of the turbulent resistivity and the stretching of the large-scale
field by shear flow. Following up on previous numerical and analytic work, this
paper presents further details of the numerical evidence for the effect, as
well as an heuristic description of how magnetic fluctuations can interact with
shear flow to produce the required electromotive force. The pressure response
of the fluid is fundamental to this mechanism, which helps explain why the
magnetic effect is stronger than its kinematic cousin, and the basic idea is
related to the well-known lack of turbulent resistivity quenching by magnetic
fluctuations. As well as being interesting for its applications to general high
Reynolds number astrophysical turbulence, where strong small-scale magnetic
fluctuations are expected to be prevalent, the magnetic shear-current effect is
a likely candidate for large-scale dynamo in the unstratified regions of
ionized accretion disks. Evidence for this is discussed, as well as future
research directions and the challenges involved with understanding details of
the effect in astrophysically relevant regimes.
