Exotic heavy fermion superconductivity in atomically thin CeCoIn₅ films

Previous studies on topological superconductivity have been mainly focused on s-wave superconductors, where fine-tuning of the Fermi energy is required. In contrast, in two-dimensional (2D) d-wave superconductors with strong spin-orbit interaction, topological superconductivity can emerge without fine-tuning the band structure due to the parity-mixed d+p wave state. Here we report an in-situ scanning tunneling microscopy study of atomically thin films of CeCoIn₅, a d-wave heavy-fermion superconductor. Both hybridization and superconducting gaps are clearly resolved even in monolayer CeCoIn₅, providing direct evidence of 2D superconductivity of heavy quasiparticles. More remarkably, in these atomically thin films, while the superconducting transition temperature is suppressed to nearly half of the bulk, the out-of-plane upper critical field is significantly enhanced and by far exceeds the Pauli and bulk orbital limits. The results reveal the emergence of exotic superconductivity such as the d+p wave state, providing a new playground for exploring topological superconductivity.