Strong-Coupling Features in $YB_6$ and $ZrB_{12}$ Studied by Point-Contact Spectroscopy

Point-contact spectroscopy studies of the superconducting energy gap and the electron-phonon coupling mechanism are performed on the boron rich $YB_6$ and $ZrB_{12}$ single crystals. The obtained values of the superconducting energy gaps suggest the strong coupling with 2 Δ/$k_{B}T_{c}$≈ 4.2 for $YB_6$ and 2 Δ/$k_{B}T_{c}$≈ 4.15 for $ZrB_{12}$. We have observed the dominant soft phonon modes mediating superconductivity in the both samples at energy ≈ 8 meV for $YB_6$ and ≈ 11 meV in $ZrB_{12}$, respectively.