Inhomogeneous superconductivity in Lu x Zr 1 − x B 12 dodecaborides with dynamic charge stripes

Physical Review B: Condensed Matter and Materials Physics. 2021. Vol. 103. No. 10. Article 104515.

Azarevich A., Bogach A., Glushkov V., Demishev S. V., Khoroshilov A.

We have studied the normal and superconductive state characteristics (resistivity, Hall coefficient, heat capacity, and magnetization) of model strongly correlated electronic systems LuxZr1−xB12 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=5–140Å and with a Cooper pair size changing nonmonotonously in the range 450–4000 Å. The parent ZrB12 and LuB12 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≤κ1,2≤6. We argue in favor of the two-band scenario of superconductivity in LuxZr1−xB12 with gap values Δ1∼14K and Δ2∼6–8K, with pairing corresponding to strong coupling limit (λe-ph∼1) in the upper band, and to weak coupling (λe-ph∼0.1–0.4) in the lower one. A pseudogap Δps-gap∼60–110K is observed in LuxZr1−xB12 above Tc. 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.

Keywords: superconductors, dynamic charge stripes, LuxZr1−xB12