Detailed Mapping of the LocalIr4+Dimers through the Metal-Insulator Transitions ofCuIr2S4Thiospinel by X-Ray Atomic P

Abstract

The evolution of the short-range structural signature of the Ir4+ dimer state in CuIr2S4 thiospinel has been studied across the metal-insulator phase transitions as the metallic state is induced by temperature, Cr doping, and x-ray fluence. An atomic pair distribution function (PDF) approach reveals that there are no local dimers that survive into the metallic phase when this is invoked by temperature and doping. The PDF shows Ir4+ dimers when they exist, regardless of whether or not they are long-range ordered. At 100 K, exposure to a 98 keV x-ray beam melts the long-range dimer order within a few seconds, though the local dimers remain intact. This shows that the metallic state accessed on warming and doping is qualitatively different from the state obtained under x-ray irradiation.

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

“…In the low temperature insulating phase of CuIr 2 S 4 pairs of Ir 4+ dimerize by moving closer together by a large 0.5 Å32 distance, resulting in the appearance of a distinct peak in the PDF at 3.0 Å40. This is shown in Fig.…”

“…This rather strong structural response allows the presence or absence of Ir 4+ dimers to be easily probed by a direct observation of this dimer peak40, and the M-shaped feature in difference curve. Dimers reveal themselves through this additional peak in the PDF irrespective of the length-scale of their ordering, allowing us to see the presence of localized charges even when they are only local in nature.…”

“…Although the MIT that takes place on warming in pure CuIr 2 S 4 is quite well understood31323637383940, the MIT on doping Cr354142 is not. The phase diagram as it is understood currently is shown in Fig.…”

Crystal structure transformation in CeRuSn seen via the atomic pair distribution function

“…In the case of subtle modifications in the atomic positions the atomic structure may be studied using a local structural probe 11,12 such as the atomic pair distribution function (PDF) analysis 13 of powder x-ray or neutron diffraction data. The chosen technique is a total scattering method because it uses all structure-relevant scattering over a large reciprocal space range of the sample.…”

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

“…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].…”