  We present a comprehensive theory on the spin- and angle-resolved
photoemission spectroscopy (SARPES) of materials with glide-mirror symmetry,
focusing on the role of glide symmetry on the spin selection rule. In the
glide-symmetric SARPES configuration, where the surface of a material, the
incoming light and the outgoing photoelectrons are invariant under a glide
reflection, the spin polarization of photoelectrons is determined by the glide
eigenvalue of the initial state, which makes SARPES a powerful tool for
studying topological phases protected by glide symmetry. We also show that, due
to the nonsymmorphic character of glide symmetry, the spin polarization of a
photoelectron whose momentum is in the second surface Brillouin zone is the
opposite of the spin polarization of a photoelectron which is ejected from the
same initial Bloch state but whose momentum is in the first zone. This momentum
dependence of spin selection rule clearly distinguishes glide symmetry from
mirror symmetry and is particularly important if the Bloch wavevector of the
initial state is close to the first surface Brillouin zone boundary. As a proof
of principle, we simulate the SARPES from the surface states of KHgSb (010) and
investigate how the spin selection rule imposed by the glide symmetry manifests
itself in a real material.
