@article{PismaZhETF.28.482,
    title = {Photon momentum in a medium with negative group velocity},
    author = {Frank, I. M.},
    journal = {Письма в ЖЭТФ},
    volume = {28},
    issue = {7},
    pages = {482},
    year = {1978},
    doi = {},
    url = {http://jetpletters.ru/ps/0/article_24195.shtml},
}