Interaction-induced topological superconductivity in antiferromagnet-superconductor junctions

We predict that junctions between an antiferromagnetic insulator and a superconductor provide a robust platform to create a one-dimensional topological superconducting state. Its emergence does not require the presence of intrinsic spin-orbit coupling nor noncollinear magnetism, but arises solely from repulsive electronic interactions on interfacial solitonic states. We demonstrate that a topological superconducting state is generated by repulsive interactions at arbitrarily small coupling strength, and that the size of the topological gap rapidly saturates to one of the parent trivial superconductor. Our results put forward antiferromagnetic insulators as a new platform for interaction-driven topological superconductivity.

Figure 1

(a) A sketch of the two-dimensional antiferromagnet (AF) and superconductor (SC) forming a one-dimensional AF-SC interface. The spectral function at the surface of the AF (b), at the surface of the SC (c), and at the interface between AF and SC (d) as given by our model Hamiltonian (1) in a honeycomb lattice. (e) The spatial distribution of the interfacial modes. Here we chose $\mathrm{\Delta }=0.3t$, $m_{\text{AF}}=0.5t$, $\mu =t$, and $V_1=V_2=0$.

Figure 2

(a) Noninteracting bands in a ribbon geometry. First neighbor interactions do not lead to a gap (b), whereas second neighbor interactions drive a gap opening (c). When both first and second neighbor interactions are present the gap remains. The parameters are $V_1=t$ in (b), $V_2=1.7t$ in (c), $V_1=t,V_2=2t$ in (d), and $m_{\text{AF}}=0.8t$, $\mathrm{\Delta }=0.4t$ in (a)–(d).

Figure 3

(a) Spectral function in the bulk in the presence of interactions, and (b) at the edge showing the emergence of a zero Majorana mode. (c) The spectral function at $\omega =0$ for a finite junction, featuring edge zero Majorana modes. We used now $\mathrm{\Delta }=0.4t$, $m_{\text{AF}}=0.8t$, $V_1=t$, and $V_2=2t$.

Figure 4

(a) Evolution of the topological gap with the electron-electron interaction: (a) As a function of $V_2$ taking $V_1=0$ and (b) as a function of $V_1$ taking $V_2=2t$. (c) The topological gap as a function of the two electronic interactions $V_1$ and $V_2$, highlighting that only the second neighbor interaction opens up a gap. We took $\mathrm{\Delta }=0.2t$ and $m_{\text{AF}}=0.4t$.