Enhanced Quasiparticle Heat Conduction in the Multigap SuperconductorLu2Fe3Si5

Thermal transport measurements have been made on the Fe-based superconductor ${\mathrm{Lu}}_{2}{\mathrm{Fe}}_{3}{\mathrm{Si}}_{5}$ (${T}_{c}\ensuremath{\sim}6\text{ }\text{ }\mathrm{K}$) down to a very low temperature ${T}_{c}/120$. The field and temperature dependences of the thermal conductivity confirm the multigap superconductivity with fully opened gaps on the whole Fermi surfaces. In comparison to ${\mathrm{MgB}}_{2}$, ${\mathrm{Lu}}_{2}{\mathrm{Fe}}_{3}{\mathrm{Si}}_{5}$ reveals a remarkably enhanced quasiparticle heat conduction in the mixed state. The results can be interpreted as a consequence of the unequal weight of the Fe $3d$-electron character among the distinct bands.