Fractional ac Josephson effect in p- and d-wave superconductors H.-J. Kwon, K. Sengupta and V. M. Yakovenko Eur. Phys. J. B, 37 3 (2004) 349-361 Published online: 02 April 2004 DOI: 10.1140/epjb/e2004-00066-4