Cu(Ir1 − xCrx)2S4: a model system for studying nanoscale phase coexistence at the metal-insulator transition

摘要

Increasingly, nanoscale phase coexistence and hidden broken symmetry statesare being found in the vicinity of metal-insulator transitions (MIT), forexample, in high temperature superconductors, heavy fermion and colossalmagnetoresistive materials, but their importance and possible role in the MITand related emergent behaviors is not understood. Despite their ubiquity, theyare hard to study because they produce weak diffuse signals in mostmeasurements. Here we propose Cu(Ir$_{1-x}$Cr$_x$)$_2$S$_4$ as a model system,where robust local structural signals lead to key new insights. We demonstratea hitherto unobserved coexistence of a Ir$^{4+}$ charge-localized dimer phaseand Cr-ferromagnetism. The resulting phase diagram that takes into account theshort range dimer order, is highly reminiscent of a generic MIT phase diagramsimilar to the cuprates. We suggest that the presence of quenched strain fromdopant ions acts as an arbiter deciding between the competing ground states.