Quantum oscillations of the superconductor LaRu2P2: Comparable mass enhancement λ ≈ 1 in Ru and Fe phosphides

We have studied the angular-dependent de Haas-van Alphen oscillations of LaRu2P2 using magnetic torque in pulsed magnetic fields up to 60 T. The observed oscillation frequencies are in excellent agreement with the geometry of the calculated Fermi surface. The temperature dependence of the oscillation amplitudes reveals effective masses m*(α) = 0.71 and m*(β) = 0.99 me, which are enhanced over the calculated band mass by λ cyc of 0.8. We find a similar enhancement of λ γ ≈ 1 in comparing the measured electronic specific heat (γ = 11. 5m J/mol K 2 ) with the total density of states from band-structure calculations. Remarkably, very similar mass enhancements have been reported in other pnictides, LaFe2P2, LaFePO (Tc ≈ 4 K), and LaRuPO, independent of whether they are superconducting or not. This is contrary to the common perceptions that the normal-state quasiparticle renormalizations reflect the strength of the superconducting pairing mechanism and leads to new questions about pairing in isostructural and isoelectronic Ru- and Fe-pnictide superconductors.