Topological band theory [closed]

Why topological insulators were discovered so late? While the band theory was known long time ago! I mean why the topological properties of electronic bands were not noticed in the past?

-
Well, physicists have a tendency to regard everything as continuous on all $\mathbb{R}$ and work with low-order pertubations as long as nothing seems to go wrong, don't we? Without really checking how mathematically sound this is... –  leftaroundabout May 9 '13 at 19:30
Mainly because spin-orbit coupling was only ever slapped on as an afterthought, from what I understand. Now that "we" are starting to seriously look into SO coupling we find all sorts of cool things, like SO Mott insulators, the TIs and the intriguing physics of the iridates... –  Lagerbaer May 9 '13 at 21:03
I think it’s worth reopening this question since this is a question asked by everyone who just enters the field of topological materials. At first there were very few review articles which focused only on current developments in the field. Now, however, more elaborate reviews (for e.g. arxiv.org/abs/1304.5693) give much more historical insight into the subject. I cannot deny the possibility of debate, arguments, etc. But there is a potential for “constructive” debate which will help many of us learn quite a bit about this exciting field. –  NanoPhys Jun 23 '13 at 13:34