Fermi Surface of the Pnictide Superconductor LaRu$_2$P$_2$ studied by quantum oscillations

LaRu$_2$P$_2$ is a stochiometric pnictide superconductor (T$_c$ $\sim$ 4.1K) and crystallizes in the ThCr$_2$Si$_2$ structure (the ``122'' pnictide family). We have mapped out its Fermi surface via the deHaas-vanAlphen effect in pulsed magnetic fields up to 60T (LANL/NHMFL). Pronounced oscillations were observed in the magnetic torque measured with a microcantilever setup. Two features are particularly noteworthy: The oscillations can be followed to surprisingly high temperatures beyond 20K, and the main frequency component at $\theta$ = 20$^{\circ}$ ($\theta$ = 0$^{\circ}$ at HIIc) is at 349T ($\alpha$-peak), significantly lower than in the related compounds LaFe$_2$P$_2$. A second frequency originating from a larger Fermi surface cross-section at 1921 T ($\beta$-peak) is identified. The temperature dependence of the amplitudes is well described by the Lifshitz- Kosevich formalism and gives low effective masses m*/m = 0.80 ($\alpha$ sheet) and 1.09 ($\beta$ sheet). Therefore, most ``122'' metals appear to have similarly low effective masses.