@article{JETPL.109.521,
    title = {},
    author = {Ruban, V. P.},
    journal = {JETP Lett.},
    volume = {109},
    issue = {8},
    pages = {512},
    year = {2019},
    doi = {},
    url = {http://jetpletters.ru/ps/dx/10.1134/S0370274X19080058},
    note = {[Pisma v ZhETF 109, 521 (2019)]}
}