Thermal Conductivity of the Pyrochlore Superconductor KOs2O6: Strong   Electron Correlations and Fully Gapped Superconductivity
  To elucidate the nature of the superconducting ground state of the geometrically frustrated pyrochlore KOs2O6 (Tc=9.6K), the thermal conductivity was measured down to low temperatures (~Tc/100). We found that the quasiparticle mean free path is strikingly enhanced below a transition at Tp=7.5K, indicating enormous electron inelastic scattering in the normal state. In a magnetic field the conduction at T ->0K is nearly constant up to ~0.4Hc2, in contrast with the rapid growth expected for superconductors with an anisotropic gap. This unambiguously indicates a fully gapped superconductivity, in contrast to the previous studies. These results highlight that KOs2O6 is unique among superconductors with strong electron correlations. 
Y.Kasahara, Y.Shimono, T.Shibauchi, Y.Matsuda, S.Yonezawa, Y.Muraoka,   and Z.Hiroi