What microscopic process produces the excess in cryogenic calorimeters?

Cryogenic calorimeters (CRESST $\mathrm{CaWO_4}$, $\mathrm{Al_2O_3}$, Si; SuperCDMS-type Si and Ge; NUCLEUS; EDELWEISS) observe a rate $\mathrm{d}R/\mathrm{d}E$ rising steeply below about 200 eV, uncorrelated with particle backgrounds and decaying after cooldown. Candidate sources include stress relaxation at holders, glue and sensor films; dislocation motion from differential thermal contraction; and annealing of radiation-induced lattice defects. An answer is a mechanism that reproduces the energy spectrum, the time dependence, the material dependence and the sensor-geometry dependence, confirmed by a controlled test that turns the excess on or off.

A detector in which removing or adding the hypothesized source (e.g., stress in the holder or film, or a defect population) changes the excess rate by a predicted factor.