Superconducting meron phase in locally noncentrosymmetric superconductors

Theory of the superconducting parity transition is extended by incorporating the vortex degree of freedom. We employ the bilayer Rashba model representing locally noncentrosymmetric layered superconductors and derive the Ginzburg-Landau free energy functional. This formulation reveals the parity transition, where the even-parity superconducting state changes to the odd-parity one upon increasing the magnetic field under the vortex states. The H-T phase diagram of CeRh₂As₂ is quantitatively reproduced and a novel superconducting state with a meron (half-skyrmion) lattice pseudospin texture is predicted.