6 Rev. Lett. 98 , 157402 (2007). Nature Phys. 3 , 192 (2007). [30] H. Hsu and L. E. Reichl, Phys. Rev. B 76 , 045418 (2007). [31] M. Kohmoto and Y. Hasegawa, Phys. Rev. B 76 , 205402 (2007). [32] L.Brey and H.A. Fertig, Phys. Rev. B 75 , 125434 (2007). [33] A. R. Akhmerov and C.W.J. Beenakker, Phys. Rev. B 77 , 085423 (2008). [26] C. Tang, W. Yan, Y. Zheng, G. Li, and L. Li, Nanotech- nology, 19 , 435401 (2008). [27] Y. Niimi, H. Kambara, T. Matsui, D. Yoshioka, and H. Fukuyama, Phys. Rev. Lett. 97 , 236804 (2006). [28] M. O. Goerbig, J. -N. Fuchs, K. Kechedzhi, and V. I. Fal’ko, Phys. Rev. Lett. 99 , 087402 (2007). [29] V. P. Gusynin, S. G. Sharapov, and J. P. Carbotte, Phys.