%0 Journal Article
%T Rotation Numbers, Boundary Forces and Gap labelling
%A J. Kellendonk
%A I. P. Zois
%J Mathematics
%D 2005
%I arXiv
%R 10.1088/0305-4470/38/18/005
%X We review the Johnson-Moser rotation number and the $K_0$-theoretical gap labelling of Bellissard for one-dimensional Schr\"odinger operators. We compare them with two further gap-labels, one being related to the motion of Dirichlet eigenvalues, the other being a $K_1$-theoretical gap label. We argue that the latter provides a natural generalisation of the Johnson-Moser rotation number to higher dimensions.
%U http://arxiv.org/abs/math-ph/0506016v1