Impact of isoelectronic substitution and hydrostatic pressure on the quantum critical properties of CeRhSi₃

There is an ongoing dispute in the community about the absence of a magnetic quantum critical point (QCP) in the noncentrosymmetric heavy fermion compound CeRhSi₃. In order to explore this question we prepared single crystals of CeRh(Si_1−xGe_x)₃ with x = 0.05 and 0.15 and determined the temperature–pressure (T–p) phase diagram by means of measurements of the electrical resistivity. The substitution of isoelectronic but large Ge enforces a lattice volume increase resulting in a weakening of the Kondo interaction. As a result, the x = 0.05 and x = 0.15 compound exhibit a transition into the antiferromagnetic (AFM) at higher temperatures being T _N = 4.7 K and T _N1 = 19.7 K, respectively. Application of pressure suppresses T _N (T _N1) monotonically and pressure induced superconductivity is observed in both Ge-substituted compounds above p ⩾ 2.16 GPa (x = 0.05) and p ⩾ 2.93 GPa (x = 0.15). Extrapolation of T _N(p) → 0 of CeRh(Si_0.95Ge_0.05)₃ yields a critical pressure of p _c ≈ 3.4 GPa (in CeRh(Si_0.85Ge_0.15)₃  p _c ≈ 3.5 GPa) pointing to the presence of an AFM QCP located deep inside the superconducting state. (paper)