@article{PismaZhETF.12.118,
    title = {Second Branch of the Spectrum of Elementary Excitations in Liquid $He^4$},
    author = {Pitaevskii, L. P.},
    journal = {πΙΣΨΝΑ Χ φότζ},
    volume = {12},
    issue = {2},
    pages = {118},
    year = {1970},
    doi = {},
    url = {http://jetpletters.ru/ps/0/article_26249.shtml},
}