Topological superconductivity in doped magnetic moiré semiconductors

Interests in excitonic mechanism for superconductivity are revived by recent advances in semiconducting heterostructures, where bound inter-layer excitons carrying twice the electron charge have been experimentally observed. In this talk, I will review general conditions for the emergence of superconductivity from these composite charged excitons and highglight why semiconducting multilayers are natural plateform for its existence. Then, using a realistic model for transition metal dichalcogenide heterobilayers, I will show that topological superconductivity can emerge upon doping the insulating magnetic state stabilized at integer filling of the topmost valence moiré band.

We shall observe that the effective attraction between charge carriers is generated by an electric p-wave Feshbach resonance arising from interlayer excitonic physics and has a tunable strength, which may be large compared to the bandwidth. Together with the low moiré carrier densities reachable by gating, this robust attraction enables access to the long-sought p-wave BEC-BCS transition. Finally, topological protection arises from an emergent time reversal symmetry emerging when the magnetic order and long wavelength magnetic fluctuations do not couple different valleys. The resulting topological superconductor features helical Majorana edge modes, leading to half-integer quantized spin-thermal Hall conductivity and to charge currents induced by circularly polarized light or other time-reversal symmetry-breaking fields.