Topological insulators and stable isomorphism versus isomorphism of vector bundles

This note gives an overview of the mathematical framework underlying topological insulators, highlighting the connection to K-theory and vector bundles. We see real'' and quaternionic’’ vector bundles arise naturally in the presence of time-reversal symmetry. Our recent results about when stable isomorphism implies isomorphism are summarised, including some ongoing work for G-equivariant K-theory for finite groups. This clarifies when K-theory completely distinguishes topological phases.