A Three-Fluid Model of Dissipation at Surfaces in Superconducting Radiofrequency Cavities
Abstract
Experiments on superconducting cavities have found that under large RF fields the quality factor can improve with increasing field amplitude, a so-called ``anti-Q slope.'' We numerically solve the Bogoliubov-de Gennes equations at a superconducting surface in a parallel magnetic field, finding at large fields there are surface quasiparticle states with energies below the bulk superconducting gap that emerge and disappear as the field cycles. Modifying the standard two-fluid model, we introduce a ``three''-fluid model where we partition the normal fluid to consider continuum and surface quasiparticle states separately. We compute dissipation in a semi-classical theory of conductivity, where we provide physical estimates of elastic scattering times of Bogoliubov quasiparticles with point-like impurities having potential strengths informed from complementary \textit{ab initio} calculations of impurities in bulk niobium. We show, in this simple yet effective framework, how the relative scattering rates of surface and continuum quasiparticle states can play a role in producing an anti-Q slope while demonstrating how this model naturally includes a mechanism for turning the anti-Q slope on and off.
Versions
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BibTeX
@misc{kelley2026threefluid,
title = {{A Three-Fluid Model of Dissipation at Surfaces in Superconducting Radiofrequency Cavities}},
author = {Matthias Liepe Michelle M. Kelley and Sean Deyo and Nathan Sitaraman and Danilo B. Liarte and Tomás Arias and James P. Sethna and Thomas Oseroff},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2608.28565},
eprint = {2608.28565},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.28565},
}
RIS
TY - UNPB
TI - A Three-Fluid Model of Dissipation at Surfaces in Superconducting Radiofrequency Cavities
AU - Matthias Liepe Michelle M. Kelley
AU - Sean Deyo
AU - Nathan Sitaraman
AU - Danilo B. Liarte
AU - Tomás Arias
AU - James P. Sethna
AU - Thomas Oseroff
PY - 2026
DA - 2026/08/28
PB - arXiv
DO - 10.48550/arxiv.2608.28565
UR - https://arxiv.org/abs/2608.28565
AB - Experiments on superconducting cavities have found that under large RF fields the quality factor can improve with increasing field amplitude, a so-called ``anti-Q slope.'' We numerically solve the Bogoliubov-de Gennes equations at a superconducting surface in a parallel magnetic field, finding at large fields there are surface quasiparticle states with energies below the bulk superconducting gap that emerge and disappear as the field cycles. Modifying the standard two-fluid model, we introduce a ``three''-fluid model where we partition the normal fluid to consider continuum and surface quasiparticle states separately. We compute dissipation in a semi-classical theory of conductivity, where we provide physical estimates of elastic scattering times of Bogoliubov quasiparticles with point-like impurities having potential strengths informed from complementary \textit{ab initio} calculations of impurities in bulk niobium. We show, in this simple yet effective framework, how the relative scattering rates of surface and continuum quasiparticle states can play a role in producing an anti-Q slope while demonstrating how this model naturally includes a mechanism for turning the anti-Q slope on and off.
ER -