Quantum Criticality in Topological Insulators and Superconductors: Emergence of Strongly Coupled Majoranas and Supersymmetry

Understand

We study symmetry breaking quantum phase transitions in topological insulators and superconductors where the single electron gap remains open in the bulk.

• Specifically, we consider spontaneous breaking of the symmetry that protects the gapless boundary modes, so that in the ordered phase these modes are gapped.
• Here we determine the fate of the topological boundary modes right at the transition where they are coupled to the strongly fluctuating order parameter field.
• Using a combination of exact solutions and renormalization group techniques, we find that the surface fermionic modes either decouple from the bulk fluctuations, or flow to a strongly coupled fixed point which remains gapless.