Topological Hamiltonian as an Exact Tool for Topological Invariants
  We propose the concept of `topological Hamiltonian' for topological insulators and superconductors in interacting systems. The eigenvalues of topological Hamiltonian are significantly different from the physical energy spectra, but we show that topological Hamiltonian contains the information of gapless surface states, therefore it is an exact tool for topological invariants. 
Zhong Wang and Binghai Yan
cond-mat.str-el hep-th