Electron Tunnelling into a Superconducting Cluster Compound: YB ₆

We performed electron tunnelling experiments into superconducting YB 6 ( T c = 7.1 K), using natural oxide as a barrier. In the second derivative of the current-voltage characteristic, we found two peaks corresponding to a shoulder around 5 meV and a peak around 8 meV, respectively, in the Eliashberg function. Our data allowed for inversion of the Eliashberg equations without consideration of proximity effects. The results indicate substantial electron-phonon coupling for the translational modes of the Y and B 6 sublattices, while the coupling to the torsional and deformational modes of the B 6 sublattice appeared to be weak.