  The Dzyaloshinskii-Moriya (DM) interaction is an antisymmetric exchange
interaction that is responsible for the emergence of chiral magnetism. The
origin of the DM interaction, however, remains to be identified albeit the
large number of studies reported on related effects. It has been recently
suggested that the DM interaction is equivalent to an equilibrium spin current
density originating from spin-orbit coupling, an effect referred to as the spin
Doppler effect. The model predicts that the DM interaction can be controlled by
spin current injected externally. Here we show that the DM exchange constant
($D$) in W/CoFeB based heterostructures can be modulated with external current
passed along the film plane. At higher current, $D$ decreases with increasing
current, which we infer is partly due to the adiabatic spin transfer torque. At
lower current, $D$ increases linearly with current regardless of the polarity
of current flow. The rate of increase in $D$ with the current density agrees
with that predicted by the model based on the spin Doppler effect. These
results imply that the DM interaction at the HM/FM interface partly originates
from an equilibrium interface spin (polarized) current which can be modulated
externally.
