Local structure and site occupancy of Cd and Hg substitutions in CeTIn5 (T=Co, Rh, Ir)

TL;DR

This study investigates how Cd and Hg atoms substitute into CeTIn5 superconductors, revealing their site preferences and how these substitutions influence electronic and magnetic properties near the superconducting phase.

Contribution

It provides detailed EXAFS measurements of atom distributions and site preferences for Cd and Hg substitutions, linking local atomic structure to bulk electronic behavior.

Findings

Cd and Hg prefer the In(1) site more than Sn.

Site occupancy varies with T and substituent type.

Substitutions significantly affect superconducting properties.

Abstract

The CeTIn5 superconductors (T=Co, Rh, or Ir) have generated great interest due to their relatively Tc's, NFL behavior, and their proximity to AF order and quantum critical points. In contrast to small changes with the T-species, electron doping in CeT(In{1-x}Mx)5 with M=Sn and hole doping with Cd or Hg have a dramatic effect on the electronic properties at very low concentrations. The present work reports EXAFS measurements that address the substituent atom distribution as a function of T, M, and x, near the superconducting phase. Together with previous measurements for M=Sn, the proportion of the M atom residing on the In(1) site, f{In(1)}, increases in the order M=Cd, Sn, and Hg, ranging from about 40% to 70%, showing a strong preference for these substituents to occupy the In(1) site (random=20%). In addition, f{In(1)} ranges from 70% to 100% for M=Hg in the order T=Co, Rh, and Ir. These fractions track the changes in the atomic radii of the various species, and help explain the sharp dependence of Tc on substituting into the In site. However, it is difficult to reconcile the small concentrations of M with the dramatic changes in the ground state in the hole-doped materials with only an impurity scattering model. These results therefore indicate that while such substitutions have interesting local atomic structures with important electronic and magnetic consequences, other local changes in the electronic and magnetic structure are equally important in determining the bulk properties of these materials.