@article{JETPL.106.539, title = {}, author = {, and , and , and Tolokonnikov, S. V.}, journal = {JETP Lett.}, volume = {106}, issue = {9}, pages = {555}, year = {2017}, doi = {}, url = {http://jetpletters.ru/ps/dx/10.7868/S0370274X17210019}, note = {[Pisma v ZhETF 106, 539 (2017)]} }