Interplay of superconductivity and charge density wave ordering in pseudoternary alloy compounds: Lu2Ir3(Si1−xGex)5, Lu2(Ir1−xRhx)3Si5, and (Lu1−xScx)2Ir3Si

Abstract

We explore the interplay and competition between superconductivity (SC) and the charge density wave (CDW) ordering transition on pseudoternary alloys ${({\text{Lu}}_{1\ensuremath{-}x}{\text{Sc}}_{x})}_{2}{\text{Ir}}_{3}{\text{Si}}_{5}$, ${\text{Lu}}_{2}{({\text{Ir}}_{1\ensuremath{-}x}{\text{Rh}}_{x})}_{3}{\text{Si}}_{5}$, and ${\text{Lu}}_{2}{\text{Ir}}_{3}{({\text{Si}}_{1\ensuremath{-}x}{\text{Ge}}_{x})}_{5}$ via magnetization, thermal and transport measurements. We track the evolution of the superconducting transition temperature ${\mathit{T}}_{\mathrm{SC}}$ and the CDW ordering transition temperature ${\mathit{T}}_{\mathrm{CDW}}$ as a function of doping concentration $x$ to present a temperature-concentration phase diagram for each of the series of compounds. We find that as we increase $x$, ${\mathit{T}}_{\mathrm{CDW}}$ and ${\mathit{T}}_{\mathrm{SC}}$ show a nonmonotonic behavior in ${\text{Lu}}_{2}{\text{Ir}}_{3}{({\text{Si}}_{1\ensuremath{-}x}{\text{Ge}}_{x})}_{5}$. Here, we observe that both CDW and SC survive till 20$%$ of the Ge substitution. In ${\text{Lu}}_{2}{({\text{Ir}}_{1\ensuremath{-}x}{\text{Rh}}_{x})}_{3}{\text{Si}}_{5}$, as Rh concentration increases, ${\mathit{T}}_{\mathrm{CDW}}$ varies rapidly from 207 to 284 K, whereas the ${\mathit{T}}_{\mathrm{SC}}$ changes gradually from 5.5 to 2.5 K. In addition, the Sc substitution at the Lu site of ${\mathrm{Lu}}_{2}\mathrm{Ir}{}_{3}{\mathrm{Si}}_{5}$ displays a slight change in CDW transition temperature, without affecting the SC ordering temperature too much. Our study reveals that the CDW anomalies are broadened and smeared out, probably by substitutional disorder effects. The heat capacity data in the vicinity of the CDW transition for all the substituted alloys are analyzed using a model of critical fluctuations in addition to a mean-field contribution and a smooth lattice background. The critical exponent changes appreciably with increasing disorder, which suggests that the first-order CDW transition in the parent compound ${\mathrm{Lu}}_{2}\mathrm{Ir}{}_{3}{\mathrm{Si}}_{5}$ changes to a second-order transition via doping.