@article{ZNSL_1995_224_a22,
     author = {V. N. Popov and P. A. Sevastianov},
     title = {Effective action and collective bose-excitations in the $t$-$J$-model},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {300--309},
     year = {1995},
     volume = {224},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1995_224_a22/}
}