  The SuperCDMS experiment implements transition-edge sensors to measure
athermal phonons produced by nuclear recoils in Ge crystals. We discuss a
numerical simulation of these TES devices and a procedure for tuning the free
model parameters to data, which reproduces superconducting-to-normal phase
separation within a TES. This tuning provides insight into the behavior of the
TESs, allows us to study the phase-separation length to optimize our detector
design, and is integrated into a more complete simulation of the phonon and
charge physics of SuperCDMS detectors.
