Topological superconductivity by doping symmetry-protected topological states

Abstract

We propose an exotic scenario in which topological superconductivity can emerge by doping strongly interacting fermionic systems whose spin degrees of freedom form a bosonic symmetry protected topological (SPT) state. Specifically, we study a one-dimensional (1D) example where the spin degrees of freedom form a spin-1 Haldane phase. Before doping, the charge and spin degrees of freedom are both gapped. Upon doping, the charge channel becomes gapless and is described by a c=1 compactified bosonic conformal field theory (CFT), while the spin channel remains gapped and still form a bosonic SPT state. Interestingly, an instability toward p-wave topological superconductivity is induced, coexisting with the symmetry protected spin edge modes that are inherited from the Haldane phase. This scenario is confirmed by density-matrix renormalization group simulation of a concrete lattice model, where we find that topological superconductivity is robust against interactions. We further show that by stacking doped Haldane phases an exotic 2D anisotropic superconductor can be realized, where the boundaries transverse to the chain direction are either gapless or spontaneously symmetry broken due to the Lieb-Schultz-Mattis (LSM) anomaly.