@article{JETPL.94.215, title = {}, author = {Val?kov, V. V. and , and Korovushkin, M. M.}, journal = {JETP Lett.}, volume = {94}, issue = {3}, pages = {197}, year = {2011}, doi = {}, url = {http://jetpletters.ru/ps/0/article_29473.shtml}, note = {[Pisma v ZhETF 94, 215 (2011)]} }