We present a detailed characterization of a new generation of athermal-phonon single-charge sensitive Si HVeV detectors, the best of which achieved 612 meV ± 4 meV baseline resolution. Our sub-eV energy resolution enables precise measurements of single-photon events and reveal consistent energy losses of 0.81 eV ± 0.03 eV per charge excitation across two facilities. We demonstrate that the noise for these detectors is well described using a standard Transition Edge Sensor noise model. We also place upper bounds on the nominal phonon collection efficiency of 45\%, establishing these detectors as the most efficient athermal phonon detectors to date, limited only by intrinsic limitations of quasiparticle generation.
@article{arxiv.2601.16307,
title = {Performance of a SuperCDMS HVeV Detector with Sub-eV Energy Resolution and Single Charge-sensitivity},
author = {Kyle Kennard and Aditi Pradeep and Mason Buchanan and Hope Fu and Aviv Simchony and Qihua Wang and Emanuele Michielin and Taylor Aralis and Elspeth Cudmore and Priscilla Cushman and Miriam Diamond and Enectali Figueroa-Feliciano and Caleb Fink and Simon Harms and Bruce A. Hines and Ziqing Hong and Martin E. Huber and Andrew Kubik and Noah Kurinsky and Rupak Mahapatra and Valentina Novati and Lekhraj Pandey and Pratyush K. Patel and Weigeng Peng and Mark Platt and Ry Pressman-Cyna and Wolfgang Rau and Runze Ren and Tyler Reynolds and James Ryan and Tarek Saab and David Sadek and Benjamin Schmidt and Zoë Smith and Sidney Stevens and Kelly Stifter and Matthew Stukel and Julius Viol and Yongqi Wang and Matthew James Wilson and Betty Young and Stefan Zatschler and Hazal Zenger and Ariel Zuñiga-Reyes},
journal= {arXiv preprint arXiv:2601.16307},
year = {2026}
}