Recent development in engineering of two-dimensional crystalline electron systems has provided a new field in the superconducting research. In particular, the artificial superlattices containing strongly correlated electron systems, such as CeCoIn₅/YbCoIn₅, CeCoIn₅/CeRhIn₅, and YbRhIn₅/CeCoIn₅/YbCoIn₅ was fabricated [1]. Bulk CeCoIn₅ is one of the typical unconventional superconductors in the vicinity of the antiferromagnetic quantum critical point. Non-Fermi liquid behaviors and d-wave superconductivity, which are characteristic of magnetic criticality, have been established. At the interface of heterostructures, Rashba-type antisymmetric spin-orbit coupling (ASOC) arises from polar inversion symmetry breaking, and therefore, the superlattice containing heavy ions is expected to be affected by the Rashba ASOC. Unique superconducting phases are expected to be realized there owing to the interplay of two-dimensional magnetic fluctuations and Rashba ASOC.

Motivated by these considerations, we study superconductivity in the two-dimensional Rashba-Hubbard model. To clarify the superconducting phase stabilized by the interplay of critical magnetic fluctuations and Rashba ASOC, we adopted fluctuation exchange approximation. We calculate the Fermi surfaces (FSs), magnetic susceptibility, and superconducting gap functions in a wide range of the filling. We show that FSs are robust against critical magnetic fluctuations in contrast to a previous theory [2]. Furthermore, we show that strongly parity-mixed superconductivity with dominant d-wave pairing is robust in a whole parameter range in contrast to the proposal in Ref. [3]. Interestingly, the parity mixing is enhanced and the subdominant spin-triplet pairing has a magnitude comparable with the spin-singlet pairing. We find signatures of the type-II van Hove singularity, such as the Lifshitz transition of FSs, strong instability to commensurate antiferromagnetic order, and the spin-triplet gap function changing from p-wave to f-wave [4].

[1] M. Shimozawa, S. K. Goh, T. Shibauchi, and Y. Matsuda, Reports on Progress in Physics 79, 074503 (2016).
[2] Y. Fujimoto, K. Miyake, and H. Matsuura, JPSJ 84, 043702 (2015).
[3] A. Greco and A. P. Schnyder, Phys. Rev. Lett. 120,177002 (2018).
[4] K. Nogaki and Y. Yanase, arXiv:2006.05952 (2020).

Keywords: strongly correlated electron systems, superconductivity, Rashba antisymmetric spin-orbit coupling, critical magnetic fluctuations