Fractional-period excitations in continuum periodic systems

H. E. Nistazakis, Mason A. Porter, P. G. Kevrekidis, D. J. Frantzeskakis, A. Nicolin, and J. K. Chin Department of Physics, University of Athens, Panepistimiopolis, Zografos, Athens 15784, Greece Department of Physics and Center for the Physics of Information, California Institute of Technology, Pasadena, California 91125, USA Department of Mathematics and Statistics, University of Massachusetts, Amherst, Massachusetts 01003-4515, USA Niels Bohr Institute, DK-2100, Blegdamsvej 17, Copenhagen, Denmark Department of Physics, MIT-Harvard Center for Ultracold Atoms, and Research Laboratory of Electronics, MIT, Cambridge, Massachusetts 02139, USA Received 26 October 2005; revised manuscript received 8 July 2006; published 18 December 2006