  The noncentrosymmetric superconductors LaPdSi3 and LaPtSi3 have been studied
with magnetization, specific heat, resistivity and muon spin
rotation/relaxation (muSR) measurements. These crystallize in the tetragonal
BaNiSn3 structure and superconductivity is observed at Tc = 2.65 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 muSR measurements reveal
that LaPdSi3 is a bulk type-I superconductor while LaPtSi3 is a type-II
material with a Ginzburg-Landau parameter of kappa = 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 Delta/kTc = 1.757(4) for LaPdSi3 and 1.735(5) for
LaPtSi3. The temperature dependence of the effective penetration depth of
LaPtSi3 was extracted from muSR measurements and was fitted giving Delta/kTc =
1.60(8) and lambda(0) = 239(3) nm. A critical field of Bc(0) = 182.7 G was
obtained for LaPdSi3 from muSR measurements, which is in good agreement with
the calculated thermodynamic critical field.
