High magnetic field superconductivity in a two-band superconductor

The simultaneous presence of superconductivity and magnetism is of great interest for the field of superconducting spintronics. Multiband superconductors can support high critical fields, and together with their high critical temperatures this makes them particularly favourable. Several recent experiments indicate critical fields exceeding theoretical predictions (see, e.g., Nature Phys 12, 139-143 (2016), Sci Rep 7, 45943 (2017), Nature 595, 526-531 (2021), arXiv:2204.12606 (2022)). Moreover, multiple theoretical works have investigated possible principles allowing for this violation (Nature Phys 12, 139 (2016), PRB 98, 144509 (2018), PRB 105, L060501 (2022)). However, an underlying general mechanism is not established.

In our work (arXiv:2208.04338 (2022)) we consider spin-splitting induced by an external in-plane magnetic field in a superconductor with two relevant bands close to the Fermi level, and show that the presence of interband superconducting pairing can promote superconductivity above the conventional limiting values of the magnetic field. Therefore, we provide evidence for a new mechanism for the limit violation.