  The 5d iridates have been the subject of much recent attention due to the
predictions of a large array of novel electronic phases driven by twisting
strong spin-orbit coupling and Hubbard correlation. As a prototype, the single
layered perovskite Sr2IrO4 was first revealed to host a Jeff=1/2 Mott
insulating state. In this material, the approximate energy scale of a variety
of interactions, involving spin-orbit coupling, magnetic exchange interaction,
and the Mott gap, allows close coupling among the corresponding physical
excitations, opening the possibility of cross control of the physical
properties. Here, we experimentally demonstrate the effective gate control of
both the transport and magnetism in a Sr2IrO4-based field effect transistor
using an ionic liquid dielectric. This approach could go beyond the
surface-limited field effect seen in conventional transistors, reflecting the
unique aspect of the Jeff=1/2 state. The simultaneous modulation of conduction
and magnetism confirms the proposed intimate coupling of charge, orbital, and
spin degrees of freedom in this oxide. These phenomena are probably related to
an enhanced deviation from the ideal Jeff=1/2 state due to the gate-promoted
conduction. The present work would have important implications in modelling the
unusual physics enabled by strong spin-orbit coupling, and provides a new route
to explore those emergent quantum phases in iridates.
