Direct observation of the quantum critical point in heavy fermion CeRhSi₃

In many heavy fermion materials the quantum critical point is masked by superconductivity and it can only be detected by use of a local probe. In the noncentrosymmetric heavy fermion CeRhSi₃ the ground state at ambient pressure is antiferromagnetically ordered and superconductivity sets in above 12 kbar coexisting with antiferromagnetism. We have unraveled a magnetic quantum critical point hidden deep inside the superconducting state of CeRhSi₃. Using the muon spin rotation technique we observed the suppression of the internal fields at the lowest measured temperature, upon increase of external pressure. Our data suggest that the ordered moments are gradually quenched with increasing pressure. At 23.6 kbar, the ordered magnetic moments are fully suppressed via a second-order phase transition, and T_N is zero.