Non-trivial Berry phase for an asymmetric one-dimensional potential in the free electron limit W.B. Hodge, E.D. Welchman and M.J. Rave Eur. Phys. J. B, 84 3 (2011) 351-355 Published online: 21 November 2011 DOI: 10.1140/epjb/e2011-20576-0