Evolution of Superconductivity and Charge Density Wave Ordering in the Lu$_5$Ir$_4$(Si$_{1-x}$Ge$_x$)$_{10}$ Alloy System

Abstract

The compounds Lu$_5$Ir$_4$Si$_{10}$ and Lu$_5$Ir$_4$Ge$_{10}$ crystallize in the tetragonal Sc$_5$Co$_4$Si$_{10}$ type structure. Lu$_5$Ir$_4$Si$_{10}$ is known to superconduct below 3.9 K and it also exhibits a strongly coupled charge density wave (CDW) transition below 83 K. Lu$_5$Ir$_4$Ge$_{10}$ undergoes a transition into the superconducting state below about 2.4 K without any CDW transition at higher temperatures. Recent Si NMR measurements on polycrystalline samples of Lu$_5$Ir$_4$Si$_{10}$ suggest that there is no energy gap at the Si site across the CDW transition. Thus it is of interest to study the evolution of the superconductivity and the CDW transition when we dope at the Si site with small quantities of Ge. Here we present the evolution of T$_C$ and T$_{CDW}$ with concentration x of Ge in the alloy system Lu$_5$Ir$_4$(Si$_{1-x}$Ge$_x$)$_{10}$ (x=0.0, 0.005, 0.01, 0.02, 0.05, 0.1, 0.2, 0.4, 1.0) as estimated from dc susceptibility measurements. We find that the CDW is strongly suppressed with increasing x and there is a simultaneous enhancement of the superconducting transition temperature T$_C$ from 3.9 K for the undoped sample to almost 6.6 K for only 10% concentration of Ge in the alloy.