Unconventional superconductivity in locally non-centrosymmetric CeNi2As2

There have recently seen intense research on heavy fermion superconductivity, inspired by the discovery of multiple superconducting phases in UTe2 and CeRh2As2. In the latter material, two superconducting phases observed under c-axis magnetic field, associated with local inversion symmetry breaking[1].

To enrich understanding of these phenomena, it is desirable to find further examples of heavy fermion superconductivity in materials with locally non-centrosymmetric structure. We have succeeded in this quest, by growing single crystals of the CaBe2Ge2 isomorph of CeNi2As2[2].

The resulting superconductivity brings more than we had expected. In addition to providing the opportunity to compare and contrast with that of CeRh2As2, the condensation occurs from an incoherent normal state quantitatively similar to that of UBe13. Our findings therefore raise profound questions not just about superconductivity in the locally non-centrosymmetric structures, but about unconventional superconductivity itself.

[1] S.Khim et al., Science 373, 1012 (2021).

[2] F. Morineau et al., arXiv:2609.35004.