We show that an in-plane Zeeman field applied to noncentrosymmetric Ising superconductors converts singlet s-wave Cooper pairs to equal-spin triplet if pairs. Singlets are converted to triplets as spins originally polarized by spin-orbit interaction are reoriented by the Zeeman field. We demonstrate that the pairing in the triplet f channel(s) decisively affects the critical field. While attraction enhances the critical field, repulsion suppresses it. The singlet to triplet conversion phenomenon has a geometrical origin, and the discussion applies universally to Ising superconductors with generic band structure such as, e.g., monolayer transition metal dichalcogenides.
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Acknowledgments. We thank G. Blumberg, T. Dvir, and H. Steinberg for enlightening discussions. We acknowledge the financial support by the Israel Science Foundation, Grant No. 1287/15 and D.M. also acknowledges the support from the Swiss National Science Foundation, Project No. 184050.
© 2019 American Physical Society.