  Axions and axion-like pseudoscalar particles with dimension-5 couplings to
photons exhibit coherent Bragg-Primakoff scattering with ordered crystals at
keV energy scales. This provides for a natural detection technique in searches
for axions produce in the Sun's interior. I will motivate the utility of dark
matter direct detection experiments in searching for solar axions, emphasizing
the role crystal-based detector technologies. I present an updated theoretical
treatment of the Bragg-Primakoff photoconversion process for keV pseudoscalars,
and address simultaneously the effects of absorption of final state photons in
crystals on the loss of coherence, which can lead to large suppressive
corrections to the event rate sensitivity for this detection technique.
However, I also show that the Borrmann effect of anomalous absorption
significantly lifts the suppression. This phenomenon is studied in Ge, NaI, and
CsI crystal experiments and its impact on the the projected sensitivities of
SuperCDMS, LEGEND, and SABRE to the solar axion parameter space. Lastly, I
investigate the future reach of multi-ton scale crystal detectors and discuss
strategies to maximize the discovery potential of experimental efforts in this
vein.
