X-ray-induced disordering of the dimerization pattern and apparent low-temperature enhancement of lattice symmetry in spinel CuIr$_2$S$_4$

TL;DR

X-ray irradiation causes a persistent structural transition in CuIr$_2$S$_4$, changing its average lattice symmetry from triclinic to tetragonal and drastically reducing electrical resistivity by disordering the dimerization pattern.

Contribution

This study reveals how x-ray exposure induces a structural transition and disordering of dimerization in CuIr$_2$S$_4$, highlighting a new way to manipulate lattice symmetry and electronic properties.

Findings

X-ray irradiation induces a transition from triclinic to tetragonal symmetry.

Electrical resistivity decreases by a factor of a thousand after irradiation.

The structural change is reversible through thermal annealing.

Abstract

At low temperatures, spinel CuIr$_2$S$_4$ is a charge-ordered spin-dimerized insulator with triclinic lattice symmetry. We find that x-rays induce a structural transition in which the local triclinic structure is preserved, but the average lattice symmetry becomes tetragonal. These structural changes are accompanied by a thousandfold reduction in the electrical resistivity. The transition is persistent, but the original state can be restored by thermal annealing. We argue that x-ray irradiation disorders the lattice dimerization pattern, producing a state in which the orientation of the dimers is preserved, but the translational long-range order is destroyed.