Planar Tunnel Spectroscopy of CeCoIn5: Study of local moment pairing using different tunnel barriers

Planar tunneling spectroscopy (PTS) measurements on the 1-1-5 heavy fermion superconductor CeCoIn₅ (Tc = 2.3 K) suggest the direct involvement of local moments in the Cooper pairing process. [1] These experiments also support the STM measurements that have shown signatures of preformed Cooper pairs above its superconducting critical temperature. [2,3]

Planar Tunnel junctions grown on CeCoIn5 with AlOx barriers confirm the persistence of preformed pairs to Tp ≈5 K and the existence of a unique field-induced gaplike feature (FIG) which increases linearly with magnetic field up to 18 T only at temperatures where pairs exist, indicating a novel interaction between the superconducting state and external fields.

To determine the barrier independence and the reproducibility of the FIG in CeCoIn5, we extend the PTS investigation with MgO as a tunnel barrier. This work offers new insights into the dependence of tunneling spectra on different tunnel barriers and helps clarify the role of magnetic field-induced excitations in the possible pairing mechanism of 1-1-5 heavy fermion superconductors.

[1] Shrestha et al., Phys. Rev. B 103, 224515 (2021).

[2] Ernst et al., Phys. Status Solidi B 247, 624 (2010).

[3] Y. Fasano et al., Physica B 536, 798 (2018).