Exposing the Odd-Parity Superconductivity in CeRh_2As_2 with Hydrostatic Pressure

Odd-parity superconductivity is a rare and sought-for state of matter with a potential for applications in topological quantum computing. Crystals with staggered locally non-centrosymmetric structures have been proposed as platforms where a magnetic field can induce a transition between even- and odd-parity superconducting (SC) states. The superconductor CeRh_2As_2 with a critical temperature T_c≈0.4 K is likely the first example material showing such a phase transition at a magnetic field μ_0H^*=4 T applied along the crystallographic c axis. CeRh_2As_2 also undergoes a phase transition of an unknown origin at T_0=0.5 K and presents signs of an antiferromagnetism below 0.25 K. Under a hydrostatic pressure of P_0≈0.5 GPa, the T_0 order vanishes, resulting in a quantum critical point. Here, using resistivity measurements under pressure, we investigate how the correlations and normal-state orders affect the SC phase switching. We find an enhancement of the in-plane critical field near P_0. At the same time, the two SC states persist well past P_0, until at least 2.7 GPa and H^* is reduced to 0.3 T, making the putative odd-parity state stable almost down to zero field.