Pressure- and Composition-Induced Structural Quantum Phase Transition in the Cubic Superconductor(Sr,Ca)3Ir4Sn13

We show that the quasi-skutterudite superconductor ${\mathrm{Sr}}_{3}{\mathrm{Ir}}_{4}{\mathrm{Sn}}_{13}$ undergoes a structural transition from a simple cubic parent structure, the $I$ phase, to a superlattice variant, the ${I}^{\ensuremath{'}}$ phase, which has a lattice parameter twice that of the high temperature phase. We argue that the superlattice distortion is associated with a charge density wave transition of the conduction electron system and demonstrate that the superlattice transition temperature ${T}^{*}$ can be suppressed to zero by combining chemical and physical pressure. This enables the first comprehensive investigation of a superlattice quantum phase transition and its interplay with superconductivity in a cubic charge density wave system.