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

Abstract

Increasingly, nanoscale phase coexistence and hidden broken symmetry states are being found in the vicinity of metal-insulator transitions (MIT), for example, in high temperature superconductors, heavy fermion and colossal magnetoresistive materials, but their importance and possible role in the MIT and related emergent behaviors is not understood. Despite their ubiquity, they are hard to study because they produce weak diffuse signals in most measurements. Here we propose Cu(Ir1 − xCrx)2S4 as a model system, where robust local structural signals lead to key new insights. We demonstrate a hitherto unobserved coexistence of an Ir4+ charge-localized dimer phase and Cr-ferromagnetism. The resulting phase diagram that takes into account the short range dimer order is highly reminiscent of a generic MIT phase diagram similar to the cuprates. We suggest that the presence of quenched strain from dopant ions acts as an arbiter deciding between the competing ground states.

Phase separation at the dimer-superconductor transition in Ir1−xRhxTe2

“…If these were related to local symmetry breaking, they would also be seen in the temperature dependent Ir ADPs in Fig. 7(b), but these exhibit canonical behavior [55,62,67,70]. Inspection of the fits of the P3m1 model to 10 K PDF data over 10Å range further corroborates this conclusion.…”

“…This simple yet powerful approach has been very successful in detecting presence of low temperature nanoscale Ir-dimer fluctuations in Cu(Ir 1−x Cr x ) 2 S 4 thiospinel [62] for Cr concentrations for which long range dimer order is not observed [72], as mentioned earlier, an information crucial for comprehensive understanding of observed anomalies in electronic transport in that system [62]. utilizing P3m1 model over 50Å range are summarized in Fig.…”

“…Here we report results of detailed local structure characterization of Ir 1−x Rh x Te 2 across the (x, T) phase diagram using x-ray total scattering based PDF approach. Ability of the PDF method to reveal hidden nanometer scale structure aspects in a broad class of complex systems, including oxides and chalcogenides, important for more thorough understanding of their physical properties is by now well established [56][57][58][59][60][61][62]. Ir 1−x Rh x Te 2 displays electronic phase diagram [31] very similar to that of other doped IrTe 2 variants, with superconductivity emerging close to x=0.1, and involves substitution of Ir by isovalent Rh with nearly identical ionic radii, thereby providing the least involved stage to explore this matter.…”

Broadening of the orbitally-induced Peierls phase transition in Cu 1−x Na x Ir 2 S 4

“…15 according to the stoichiometric ratio with 1 wt% excess S. The mixed powder samples sealed in vacuumed quartz tubes were sintered at 1123 K for 8 days. The samples were cooled down to room temperature slowly.…”

“…It has been demonstrated that the spin-orbital coupling, which exists widely in the iridium-based materials, plays an important role in these extraordinary physical properties [11]. Especially, the spinel sulphide CuIr 2 S 4 is well known as an orbitally-induced Peierls phase transition, which provides a prototype to investigate the interplay between charge, spin, orbital and lattice degrees of freedom [12][13][14][15].…”