  Crystal defects can highlight interesting quantum features by coupling to the
low-energy Hamiltonian $H$. Here we show that independently of this $H$
coupling, topological crystalline defects can generate new features by directly
modifying the response theory of electric field probes such as Raman
scattering. To show this we consider an antiferromagnetic spin-1/2 model
$H_{spin}$ on a zigzag chain. Crystalline domain walls between two zigzag
domains appear as at most local defects in $H_{spin}$, but as topological (not
locally creatable) defects in the Raman operator $R$ of inelastic photon
scattering. Using time evolving block decimation (TEBD) numerics, mean field,
and bosonization, we show that a finite density of crystalline domain walls
shifts the entire Raman signal to produce an effective gap. This
lattice-defect-induced Raman gap closes and reopens in applied magnetic fields.
We discuss the effect in terms of photons sensing the lattice defects within
$R$ as spin-dimerization domain walls, with $Z_2$ character, and a resulting
shift of the probed wavevector from $q=0$ to $\pi+\delta q$, giving an
$\textit{O}(1)$ change in contrast to local defects. The magneto-Raman
singularity from topological lattice defects here relies on the $H_{spin}$
spinon liquid state, suggesting future applications using lattice topological
defects to modify response-theory operators independently of $H$ and thereby
generate new probes of quantum phases.
