Modeling Athermal Phonons in Novel Materials using the G4CMP Simulation Toolkit

Understanding phonon and charge propagation in superconducting devices plays an important role in both performing low-threshold dark matter searches and limiting correlated errors in superconducting qubits. The Geant4 Condensed Matter Physics (G4CMP) package, originally developed for the Cryogenic Dark Matter Search (CDMS) experiment, models charge and phonon transport within silicon and germanium detectors and has been validated by experimental measurements of phonon caustics, mean charge-carrier drift velocities, and heat pulse propagation times. In this work, we present a concise framework for expanding the capabilities for phonon transport to a number of other novel substrate materials of interest to the dark matter and quantum computing communities, including sapphire Al$₂$O$₃$, gallium arsenide (GaAs), lithium fluoride (LiF), calcium tungstate CaWO$₄$, and calcium fluoride CaF$₂$. We demonstrate the use of this framework in generating phonon transport properties of these materials and compare these properties with experimentally-determined values where available.