@article{wada1958,
  title={Exact Treatment of Bardeen's Theory of Superconductivity in the Strong Coupling Limit},
  author={Yasushi Wada and Fumihiko Takano and Nobuyuki Fukuda},
  year={1958},
  journal={Progress of Theoretical Physics},
  doi={10.1143/ptp.19.597},
  url={https://doi.org/10.1143/ptp.19.597}
}