Transverse-field muon spin relaxation investigations of the magnetic penetration depth in. the carbide superconductors Y2C2(Br,I)(2) and YC2

We present measurements of the temperature and magnetic field (B-ext < 0.2 T) dependences of the transverse-field muon spin relaxation rate taken on p olycrystalline samples of the layered superconductors Y2C2X2, X = Br,I, and the binary carbide YC2. The aim of these investigations was to determine t he magnetic penetration depth <lambda>(T) which is a fundamental parameter of the superconducting state. The magnetic-field dependence of the muon-dep olarization rate below T-c is discussed. An analysis of the temperature dep endence df the depolarization rates allows qualitative conclusions regardin g the strength of the electron-phonon coupling in the compounds under inves tigation. The dependence of the transition temperature on the condensate de nsity of the halide-carbide superconductors is compared to that of other ex otic superconductors.