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

The magnetic shear-current effect: generation of large-scale magnetic fields by the small-scale dynamo