We have studied the normal and superconductive state characteristics (resistivity, Hall coefficient, heat capacity, and magnetization) of model strongly correlated electronic systems ${\mathrm{Lu}}_x{\mathrm{Zr}}_{1-x}{\mathrm{B}}_{12}$ with cooperative Jahn-Teller instability of the boron rigid cage and with dynamic charge stripes. It was found that these metals are s-wave dirty limit superconductors with a small mean free path of charge carriers $l=5–140\AA$ and with a Cooper pair size changing nonmonotonously in the range 450–4000 Å. The parent ${\mathrm{ZrB}}_{12}$ and ${\mathrm{LuB}}_{12}$ borides are type-I superconductors, and Zr to Lu substitution induces a type-I to type-II phase transition providing a variation of the Ginzburg-Landau-Maki parameter in the limits $0.65\le {\kappa }_{1,2}\le 6$. We argue in favor of the two-band scenario of superconductivity in ${\mathrm{Lu}}_x{\mathrm{Zr}}_{1-x}{\mathrm{B}}_{12}$ with gap values ${\mathrm{\Delta }}_1\sim 14\mathrm{K}$ and ${\mathrm{\Delta }}_2\sim 6–8\mathrm{K}$, with pairing corresponding to strong coupling limit $({\lambda }_{\text{e-ph}}\sim 1)$ in the upper band, and to weak coupling $({\lambda }_{\text{e-ph}}\sim 0.1–0.4)$ in the lower one. A pseudogap ${\mathrm{\Delta }}_{\text{ps-gap}}\sim 60–110\mathrm{K}$ is observed in ${\mathrm{Lu}}_x{\mathrm{Zr}}_{1-x}{\mathrm{B}}_{12}$ above $T_c$. We discuss also the possibility of anisotropic single-band superconductivity with stripe-induced both pair breaking and anisotropy, and analyze the origin of a unique enhanced surface superconductivity detected in these model compounds.

• Received 21 December 2020
• Revised 1 March 2021
• Accepted 9 March 2021

DOI:https://doi.org/10.1103/PhysRevB.103.104515