@article{brusov_brusov_majumdar_orehova_2003,  title={Ultrasound attenuation and collective modes in mixed d x2-y2 + id xy state of unconventional superconductors},  volume={33},  ISSN={0103-9733},  url={https://doi.org/10.1590/S0103-97332003000400018},  DOI={10.1590/S0103-97332003000400018},  number={4},  journal={Brazilian Journal of Physics},  publisher={Sociedade Brasileira de Física},  author={Brusov, Peter and Brusov, Paul and Majumdar, Pinaki and Orehova, Natali},  year={2003},  month={Dec},  pages={729–732} }