  We study the holographic dual of fermions interacting in a
Schwarzschild-AdS$_{d+1}$ background via a dipole (Pauli) coupling sourced by a
probe gauge field. We find quite generally that a gap forms in the dual
operator spectrum as the Pauli coupling is strengthened. Previous
investigations have observed this behavior in analogous constructions with
Reissner-Nordstr\"om-AdS (RN-AdS$_4$) backgrounds, but the emergence of
log-oscillatory behavior in those models' spectra prevented identification of
the underlying gapping mechanism. Our model obviates this issue through its
modified geometry and traces the gapping mechanism back to the bulk dynamics.
We show in general that there is a duality between zeros for large positive
values of the coupling and poles in the spectrum for equivalent couplings but
with opposite sign as seen recently in the RN-AdS$_4$ background\cite{alsup}.
The duality arises from the two possible quantizations for computing the
retarded propagator. Coupled with the earlier string
results\cite{gauntlett,gubser2} that Fermi surfaces are generally absent from
the spectral function, our finding that the Pauli term engineers the gap
suggests that the model examined here offers a way of studying non-perturbative
physics in fermionic matter at finite density typified by Mott insulating
systems.
