Thermal Conductivity of the Pyrochlore Superconductor KOs2O6: Strong Electron Correlations and Fully Gapped Superconductivity

TL;DR

This study reveals that the pyrochlore superconductor KOs2O6 exhibits fully gapped superconductivity with strong electron correlations, characterized by enhanced quasiparticle mean free path and isotropic gap behavior at low temperatures.

Contribution

It provides new evidence for fully gapped superconductivity in KOs2O6, contrasting previous studies and highlighting its unique properties among strongly correlated superconductors.

Findings

Quasiparticle mean free path is greatly enhanced below Tp=7.5K.

Conduction remains nearly constant up to ~0.4Hc2 at T -> 0K.

Superconductivity in KOs2O6 is fully gapped, not anisotropic.

Abstract

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.