What is the discovery?
Iridium oxides with strong spin-orbit coupling are fertile ground for the pursuit of new states of quantum matter. Recently, an exotic “Tomonaga-Luttinger spin liquid” phase was proposed to exist in Ba4Ir3O10, a compound with a crystal structure built of iridium trimers. In a new paper appearing in Physical Review B, a team lead by Xiang Chen from Berkeley and Yu He from Yale report detailed investigations of low temperature charge and magnetic superstructures in Ba4Ir3O10. Contrary to previous reports, they discover a series of phase transitions to different long-range ordered states, without evidence of the proposed liquid-like magnetic correlations. Resonant elastic x-ray scattering measurements allow the identification of distinct structural and magnetic transitions and resolve the symmetries of these new phases.
Why is it important?
Previous reports of a lack of magnetic ordering in this compound, despite strong magnetic interactions and no obvious mechanism for frustration in the crystal structure, hinted at some new physical mechanism governing the formation of quantum ground state. The work of Chen et al deviates from these previous findings in two important ways. First, they find that the crystal structure is distorted relative to the room temperature structure, and second, they find that the iridium moments do indeed order magnetically at low temperature. Identifying these ordering instabilities is essential for developing an understanding of the energetics of Ba4Ir3O10. Although it is not yet clear why some research groups observe magnetic order, and others do not, it is nevertheless essential that the symmetry of the low-energy ordered states are now understood.
Why did this research need CHEXS?
The QM2 beamline at CHEXS is dedicated to uncovering and characterizing subtle ordered states in quantum materials at low temperatures. This work required several experiments, both at the QM2 beamline at CHEXS and beamline 6IDB at the APS, to sort out the subtle details of the structural and magnetic ordering transitions. Weak superstructure peaks form a complex pattern in reciprocal space, which requires the ability to survey wide regions and zoom in on fine details. X-rays are the tool of choice to understand coupled charge and magnetic transitions in small crystals of iridium oxides, which are ill-suited to investigations with neutrons.
How was the work funded?
Work at Lawrence Berkeley National Laboratory was funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under Contract No. DE-AC02-05-CH11231 within the Quantum Materials Program (KC2202). Y.H. acknowledges support from the Miller Institute for Basic Research in Science. A.F. acknowledges support from the Alfred P. Sloan Fellowship in Physics. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility, operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Extraordinary facility operations were supported in part by the DOE Office of Science through the National Virtual Biotechnology Laboratory, a consortium of DOE national laboratories focused on the response to COVID-19, with funding provided by the Coronavirus CARES Act. This work is based upon research conducted at the Center for High Energy X-ray Sciences (CHEXS) which is supported by the National Science Foundation under award DMR-1829070.
Structural and magnetic transitions in the planar antiferromagnet Ba4Ir3O10
Xiang Chen, Yu He, Shan Wu, Yu Song, Dongsheng Yuan, Edith Bourret-Courchesne, Jacob PC Ruff, Zahirul Islam, Alex Frano, and Robert J Birgeneau
Phys. Rev. B 103, 224420 (2021); https://doi.org/10.1103/PhysRevB.103.224420