Inhomogeneous superconductivity in LuxZr1-xB12 dodecaborides with dynamic charge stripes

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 = 5-140 angstrom and with a Cooper pair size changing nonmonotonously in the range 450-4000 angstrom. 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 <= kappa(1,2) <= 6. We argue in favor of the two-band scenario of superconductivity in LuxZr1-xB12 with gap values Delta(1) similar to 14K and Delta(2) similar to 6-8K, with pairing corresponding to strong coupling limit (lambda(e-ph) similar to 1) in the upper band, and to weak coupling (lambda(e-ph) similar to 0.1-0.4) in the lower one. A pseudogap Delta(ps-gap) similar to 60-110K is observed in LuxZr1-xB12 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.

Automated summary

LuxZr1-xB12 exhibits s-wave dirty limit superconductivity with influences from Jahn-Teller instability and dynamic charge stripes. Zr to Lu substitution induces a transition from type-I to type-II superconductors, affecting the superconducting properties.