  Adiabatic spin transfer torque induced domain wall (DW) depinning from a
notch and DW propagation in a nanowire with a series of notches is
investigated. Surprisingly, notches help a current to depin a DW and make a DW
easier to propagate along a wire. Following fascinating results on DW dynamics
are found. 1) The depinning current density of a DW in a notch is substantially
lower than the intrinsic threshold value below which a sustainable DW
propagation doesn't exist in a homogeneous wire. 2) The DW displacement from a
notch is insensitive to notch geometry and current density when it is between
the depinning and the intrinsic threshold current density. 3) A current density
below the intrinsic threshold value can induce a sustainable DW propagation
along notched nanowires. These findings not only reveal interesting and
complicated interaction between a current and a DW, but also have profound
implications in our current understanding of current-driven DW dynamics as well
as in the design of spintronic devices.
