  Electron transport in magnetic orders and the magnetic orders dynamics have a
mutual dependence, which provides the key mechanisms in spin-dependent
phenomena. Recently, antiferromagnetic orders are focused on as the magnetic
order, where current-induced spin-transfer torques, a typical effect of
electron transport on the magnetic order, have been debatable mainly because of
the lack of an analytic derivation based on quantum field theory. Here, we
construct the microscopic theory of spin-transfer torques on the slowly-varying
staggered magnetization in antiferromagnets with weak canting. In our theory,
the electron is captured by bonding/antibonding states, each of which is the
eigenstate of the system, doubly degenerates, and spatially spreads to
sublattices because of electron hopping. The spin of the eigenstates depends on
the momentum in general, and a nontrivial spin-momentum locking arises for the
case with no site inversion symmetry, without considering any spin-orbit
couplings. The spin current of the eigenstates includes an anomalous component
proportional to a kind of gauge field defined by derivatives in momentum space
and induces the adiabatic spin-transfer torques on the magnetization.
Unexpectedly, we find that one of the nonadiabatic torques has the same form as
the adiabatic spin-transfer torque, while the obtained forms for the adiabatic
and nonadiabatic spin-transfer torques agree with the phenomenological
derivation based on the symmetry consideration. This finding suggests that the
conventional explanation for the spin-transfer torques in antiferromagnets
should be changed. Our microscopic theory provides a fundamental understanding
of spin-related physics in antiferromagnets.
