Superconducting properties of the hexagonal layered molybdenum carbide $\eta $-Mo$_{3}$C$_{2}$

Superconductivity of $\eta $-Mo$_{3}$C$_{2}$ ($T_{c}$=8.5K) was reported in 1960s, while detailed superconducting and structure properties remained uncertain probably because those were complicated somewhat by carbon non-stoichiometry, partially thermal decomposition, and so on. Recently, we found the degree of problems is fairly reduced by employing high-pressure method, resulting in a distinct sample quality-improvement, which allowed us to conduct neutron diffraction, magnetic susceptibility, and specific-heat measurements on a polycrystalline form of $\eta $-Mo$_{3}$C$_{2}$ [1]. A significant layered character was found in the structure, which comprises edge-sharing CMo$_{6}$ octahedra sheets and $\sim $50{\%} carbon occupied blocks. Magnetic characterization revealed the Ginzburg-Landau parameter of $\eta $-Mo$_{3}$C$_{2}$ is $\sim $26, which is close to that for the comparable $T_{c}$ compound Li$_{2}$Pd$_{3}$B ($\sim $21), but less than a half of that for MgCNi$_{3}$ ($\sim $54). \newline \newline [1] K. Yamaura et al., PRB 74, 184510 (2006).