Investigations of the superconducting states of noncentrosymmetric LaPdSi 3 and LaPtSi 3

The noncentrosymmetric superconductors LaPdSi3 and LaPtSi3 have been studied with magnetization, specific-heat, resistivity, and μSR measurements. These crystallize in the tetragonal BaNiSn3 structure and superconductivity is observed at Tc=2.65(5) K for LaPdSi3 and Tc=1.52(6) K for LaPtSi3. The results are consistent with both compounds being weakly coupled, fully gapped superconductors but μSR measurements reveal that LaPdSi3 is a bulk type-I superconductor while LaPtSi3 is a type-II material with a Ginzburg-Landau parameter of κ=2.49(4). This is further supported by specific-heat measurements, where the transition in an applied field is first order in LaPdSi3 but second order in LaPtSi3. The electronic specific heat in the superconducting state was analyzed using an isotropic s-wave model that gave Δ0/kBTc=1.757(4) for LaPdSi3 and 1.735(5) for LaPtSi3. The temperature dependence of the effective penetration depth [λeff(T)] of LaPtSi3 was extracted from μSR measurements and was fitted giving Δ0/kBTc=1.60(8) and λeff(0)=239(3) nm. A critical field of Bc(0) = 182.7 G was obtained for LaPdSi3 from μSR measurements, which is in good agreement with the calculated thermodynamic critical field.