Inhomogeneous superconductivity in LuxZr1-xB12 dodecaborides with dynamic charge stripes

TL;DR

This study investigates the superconducting properties of LuxZr1-xB12 borides, revealing inhomogeneous superconductivity, a two-band scenario, and the influence of dynamic charge stripes on their electronic behavior.

Contribution

It introduces a two-band superconductivity model with strong and weak coupling in LuxZr1-xB12 and discusses the role of dynamic charge stripes and inhomogeneity.

Findings

LuxZr1-xB12 are s-wave dirty limit superconductors.

A pseudogap of 60-110 K exists above Tc.

Type-I to type-II transition occurs with Zr to Lu substitution.

Abstract

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 A and with a Cooper pair size changing non-monotonously in the range 450 - 4000 A. The parent ZrB12 and LuB12 borides are type-I superconductors, and Zr to Lu substitution induces a type-I - type-II phase transition providing a variation of the Ginzburg-Landau-Maki parameter in the limits 0.65 < kappa1,2 < 6. We argue in favor of the two-band scenario of superconductivity in LuxZr1-xB12 with gap values Delta_1 ~ 14 K and Delta_2 ~ 6 - 8 K, with pairing corresponding to strong coupling limit (lambda_e-ph ~ 1) in the upper band, and to weak coupling (lambda_e-ph ~ 0.1 - 0.4) in the lower one. A pseudogap Delta_ps-gap ~ 60 - 110 K 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 unique enhanced surface superconductivity detected in these model compounds.