Title: Multiphase superconductivity in CeRh2As2
I will report on the discovery of CeRh2As2, a new heavy fermion superconductor with a Tc of 0.26 K. In the normal state, an anomaly at 0.4 K points to an ordered state of unknown character, without signatures in magnetic probes. The superconducting state has huge and anisotropic critical fields: 14 T for magnetic fields in the c-direction and 2 T for inplane fields. Most interestingly, a field-induced phase transition within the superconducting state appears for c-axis fields in magnetisation, susceptibility and magnetostriction. We find that the low-field state is Pauli limited with enhanced critical fields. When this state is suppressed, a purely orbitally limited high-field superconducting state appears. The phase diagram can be understood by taking into account the local symmetry at the Ce position, where inversion symmetry is broken although CeRh2As2 is globally centrosymmetric. This leads to staggered Rashba spin-orbit coupling, and the field drives a transition from even to odd parity superconductivity.