Generic Symmetry Breaking Instability of Topological Insulators due to a   Novel van Hove Singularity
  We point out that in the deep band-inverted state, topological insulators are generically vulnerable against symmetry breaking instability, due to a divergently large density of states of 1D-like exponent near the chemical potential. This feature at the band edge is associated with a novel van Hove singularity resulting from the development of a Mexican-hat band dispersion. We demonstrate this generic behavior via prototypical 2D and 3D models. This realization not only explains the existing experimental observations of additional phases, but also suggests a route to activate additional functionalities to topological insulators via ordering, particularly for the long-sought topological superconductivities. 
Xu-Gang He, Xiaoxiang Xi and Wei Ku
cond-mat.mes-hall cond-mat.mtrl-sci