Spin-triplet superconductivity from excitonic effect in doped insulators

Despite being of fundamental importance and potential interest for topological quantum computing, spin-triplet superconductors remain rare in solid state materials after decades of research. In this work, we present a three-particle mechanism for spin-triplet superconductivity in multiband systems, where an effective attraction between doped electrons is produced from the Coulomb repulsion via a virtual interband transition involving a third electron [V. Crepel, L. Fu, Sci. Adv. 7, eabh2233 (2021)]. Our theory is analytically controlled by an interband hybridization parameter and explicitly demonstrated in doped band insulators with the example of an extended Hubbard model. Our theory of exciton-mediated pairing reveals how, as a matter of principle, a two-particle bound state can arise from the strong electron repulsion upon doping, opening a viable path to Bose-Einstein condensate (BEC)-Bardeen-Cooper-Schrieffer (BCS) physics in solid state systems. In light of this theory, we propose that recently discovered dilute superconductors such as ZrNCl, WTe2, and moire materials can be spin-triplet and compare the expected consequences of our theory with experimental data.

Automated summary

Despite being rare, spin-triplet superconductors are of fundamental importance and potential interest for topological quantum computing. In this work, a three-particle mechanism for spin-triplet superconductivity is proposed, where an effective attraction between doped electrons is generated from the Coulomb repulsion through a virtual interband transition involving a third electron. This theory reveals the possibility of a two-particle bound state arising from the strong electron repulsion upon doping, providing a new pathway to Bose-Einstein condensate (BEC)-Bardeen-Cooper-Schrieffer (BCS) physics in solid state systems.