1. N. D. Kuz’michev and M. A. Vasyutin, Fiz. Tverd. Tela (St. Petersburg) 40(2), 202 (1998) [Phys. Solid State 40 (2), 180 (1998)].
2. T. S. Orlova, B. I. Smirnov, and J. Y. Laval, Fiz. Tverd. Tela (St. Petersburg) 40(7), 1195 (1998) [Phys. Solid State 40 (7), 1088 (1998)].
3. C. Franzese, V. Cataudella, S. E. Korshunov, and R. Fazio, Phys. Rev. B: Condens. Matter 62, 9287 (2000).
4. J. Kotzler, D. Gorlitz, S. Skwirblies, and A. Wriedt, Phys. Rev. Lett. 87, 127005 (2001).
5. A. N. Artemov and Yu. V. Medvedev, Fiz. Nizk. Temp. (Kharkov) 28(4), 349 (2002) [Low Temp. Phys. 28 (4), 242 (2002)].