1306.1816 (Hermann Schulz-Baldes et al.)

Invariants for J-unitaries on Real Krein spaces and the classification
of transfer operators    [PDF]

Hermann Schulz-Baldes, Carlos Villegas-Blas

Essentially S^1-gapped J-unitaries on a Krein space (K,J) conserving, moreover, a Real structure, are shown to possess Z or Z_2-valued homotopy invariants which can be expressed in terms of Krein inertia of the eigenvalues on the unit circle and are rooted in a detailed analysis of their collisions. When applied to the transfer operators associated with periodic two-dimensional tight-binding Hamiltonians, these new invariants determine the existence and nature of the surface modes (Majorana or conventional fermions, chirality) and allow to distinguish different phases of various topological insulators.

View original: http://arxiv.org/abs/1306.1816